On 04/05, Robert Bragg wrote:
> Enables access to OA unit metrics for BDW, CHV, SKL and BXT which all
> share (more-or-less) the same OA unit design.
>
> Of particular note in comparison to Haswell: some OA unit HW config
> state has become per-context state and as a consequence it is somewhat
> more complicated to manage synchronous state changes from the cpu while
> there's no guarantee of what context (if any) is currently actively
> running on the gpu.
>
> The periodic sampling frequency which can be particularly useful for
> system-wide analysis (as opposed to command stream synchronised
> MI_REPORT_PERF_COUNT commands) is perhaps the most surprising state to
> have become per-context save and restored (while the OABUFFER
> destination is still a shared, system-wide resource).
>
> This support for gen8+ takes care to consider a number of timing
> challenges involved in synchronously updating per-context state
> primarily by programming all config state from the cpu and updating all
> current and saved contexts synchronously while the OA unit is still
> disabled.
>
> The driver intentionally avoids depending on command streamer
> programming to update OA state considering the lack of synchronization
> between the automatic loading of OACTXCONTROL state (that includes the
> periodic sampling state and enable state) on context restore and the
> parsing of any general purpose BB the driver can control. I.e. this
> implementation is careful to avoid the possibility of a context restore
> temporarily enabling any out-of-date periodic sampling state. In
> addition to the risk of transiently-out-of-date state being loaded
> automatically; there are also internal HW latencies involved in the
> loading of MUX configurations which would be difficult to account for
> from the command streamer (and we only want to enable the unit when once
> the MUX configuration is complete).
>
> Since the Gen8+ OA unit design no longer supports clock gating the unit
> off for a single given context (which effectively stopped any progress
> of counters while any other context was running) and instead supports
> tagging OA reports with a context ID for filtering on the CPU, it means
> we can no longer hide the system-wide progress of counters from a
> non-privileged application only interested in metrics for its own
> context. Although we could theoretically try and subtract the progress
> of other contexts before forwarding reports via read() we aren't in a
> position to filter reports captured via MI_REPORT_PERF_COUNT commands.
> As a result, for Gen8+, we always require the
> dev.i915.perf_stream_paranoid to be unset for any access to OA metrics
> if not root.
>
> Signed-off-by: Robert Bragg <rob...@sixbynine.org>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 45 +-
> drivers/gpu/drm/i915/i915_gem_context.h | 1 +
> drivers/gpu/drm/i915/i915_perf.c | 938
> +++++++++++++++++++++++++++++---
> drivers/gpu/drm/i915/i915_reg.h | 22 +
> drivers/gpu/drm/i915/intel_lrc.c | 5 +
> include/uapi/drm/i915_drm.h | 19 +-
> 6 files changed, 937 insertions(+), 93 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 9c37b73ac7ac..3a22b6fd0ee6 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2067,9 +2067,17 @@ struct i915_oa_ops {
> void (*init_oa_buffer)(struct drm_i915_private *dev_priv);
>
> /**
> - * @enable_metric_set: Applies any MUX configuration to set up the
> - * Boolean and Custom (B/C) counters that are part of the counter
> - * reports being sampled. May apply system constraints such as
> + * @select_metric_set: The auto generated code that checks whether a
> + * requested OA config is applicable to the system and if so sets up
> + * the mux, oa and flex eu register config pointers according to the
> + * current dev_priv->perf.oa.metrics_set.
> + */
> + int (*select_metric_set)(struct drm_i915_private *dev_priv);
> +
> + /**
> + * @enable_metric_set: Selects and applies any MUX configuration to set
> + * up the Boolean and Custom (B/C) counters that are part of the
> + * counter reports being sampled. May apply system constraints such as
> * disabling EU clock gating as required.
> */
> int (*enable_metric_set)(struct drm_i915_private *dev_priv);
> @@ -2100,20 +2108,13 @@ struct i915_oa_ops {
> size_t *offset);
>
> /**
> - * @oa_buffer_check: Check for OA buffer data + update tail
> - *
> - * This is either called via fops or the poll check hrtimer (atomic
> - * ctx) without any locks taken.
> + * @oa_hw_tail_read: read the OA tail pointer register
> *
> - * It's safe to read OA config state here unlocked, assuming that this
> - * is only called while the stream is enabled, while the global OA
> - * configuration can't be modified.
> - *
> - * Efficiency is more important than avoiding some false positives
> - * here, which will be handled gracefully - likely resulting in an
> - * %EAGAIN error for userspace.
> + * In particular this enables us to share all the fiddly code for
> + * handling the OA unit tail pointer race that affects multiple
> + * generations.
> */
> - bool (*oa_buffer_check)(struct drm_i915_private *dev_priv);
> + u32 (*oa_hw_tail_read)(struct drm_i915_private *dev_priv);
> };
>
> struct intel_cdclk_state {
> @@ -2475,6 +2476,7 @@ struct drm_i915_private {
> struct {
> struct i915_vma *vma;
> u8 *vaddr;
> + u32 last_ctx_id;
> int format;
> int format_size;
>
> @@ -2544,6 +2546,14 @@ struct drm_i915_private {
> } oa_buffer;
>
> u32 gen7_latched_oastatus1;
> + u32 ctx_oactxctrl_offset;
> + u32 ctx_flexeu0_offset;
> +
> + /* The RPT_ID/reason field for Gen8+ includes a bit
> + * to determine if the CTX ID in the report is valid
> + * but the specific bit differs between Gen 8 and 9
> + */
> + u32 gen8_valid_ctx_bit;
>
> struct i915_oa_ops ops;
> const struct i915_oa_format *oa_formats;
> @@ -2854,6 +2864,8 @@ intel_info(const struct drm_i915_private *dev_priv)
> #define IS_KBL_ULX(dev_priv) (INTEL_DEVID(dev_priv) == 0x590E || \
> INTEL_DEVID(dev_priv) == 0x5915 || \
> INTEL_DEVID(dev_priv) == 0x591E)
> +#define IS_SKL_GT2(dev_priv) (IS_SKYLAKE(dev_priv) && \
> + (INTEL_DEVID(dev_priv) & 0x00F0) == 0x0010)
> #define IS_SKL_GT3(dev_priv) (IS_SKYLAKE(dev_priv) && \
> (INTEL_DEVID(dev_priv) & 0x00F0) == 0x0020)
> #define IS_SKL_GT4(dev_priv) (IS_SKYLAKE(dev_priv) && \
> @@ -3605,6 +3617,9 @@ i915_gem_context_lookup_timeline(struct
> i915_gem_context *ctx,
>
> int i915_perf_open_ioctl(struct drm_device *dev, void *data,
> struct drm_file *file);
> +void i915_oa_update_reg_state(struct intel_engine_cs *engine,
> + struct i915_gem_context *ctx,
> + uint32_t *reg_state);
>
> /* i915_gem_evict.c */
> int __must_check i915_gem_evict_something(struct i915_address_space *vm,
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.h
> b/drivers/gpu/drm/i915/i915_gem_context.h
> index 4af2ab94558b..3f4ce73bea43 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.h
> +++ b/drivers/gpu/drm/i915/i915_gem_context.h
> @@ -151,6 +151,7 @@ struct i915_gem_context {
> u64 lrc_desc;
> int pin_count;
> bool initialised;
> + atomic_t oa_state_dirty;
> } engine[I915_NUM_ENGINES];
>
> /** ring_size: size for allocating the per-engine ring buffer */
> diff --git a/drivers/gpu/drm/i915/i915_perf.c
> b/drivers/gpu/drm/i915/i915_perf.c
> index 3277a52ce98e..98eb6415b63a 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -196,6 +196,12 @@
>
> #include "i915_drv.h"
> #include "i915_oa_hsw.h"
> +#include "i915_oa_bdw.h"
> +#include "i915_oa_chv.h"
> +#include "i915_oa_sklgt2.h"
> +#include "i915_oa_sklgt3.h"
> +#include "i915_oa_sklgt4.h"
> +#include "i915_oa_bxt.h"
>
> /* HW requires this to be a power of two, between 128k and 16M, though driver
> * is currently generally designed assuming the largest 16M size is used such
> @@ -215,7 +221,7 @@
> *
> * Although this can be observed explicitly while copying reports to
> userspace
> * by checking for a zeroed report-id field in tail reports, we want to
> account
> - * for this earlier, as part of the _oa_buffer_check to avoid lots of
> redundant
> + * for this earlier, as part of the oa_buffer_check to avoid lots of
> redundant
> * read() attempts.
> *
> * In effect we define a tail pointer for reading that lags the real tail
> @@ -237,7 +243,7 @@
> * indicates that an updated tail pointer is needed.
> *
> * Most of the implementation details for this workaround are in
> - * gen7_oa_buffer_check_unlocked() and gen7_appand_oa_reports()
> + * oa_buffer_check_unlocked() and _append_oa_reports()
> *
> * Note for posterity: previously the driver used to define an effective tail
> * pointer that lagged the real pointer by a 'tail margin' measured in bytes
> @@ -272,6 +278,13 @@ static u32 i915_perf_stream_paranoid = true;
>
> #define INVALID_CTX_ID 0xffffffff
>
> +/* On Gen8+ automatically triggered OA reports include a 'reason' field... */
> +#define OAREPORT_REASON_MASK 0x3f
> +#define OAREPORT_REASON_SHIFT 19
> +#define OAREPORT_REASON_TIMER (1<<0)
> +#define OAREPORT_REASON_CTX_SWITCH (1<<3)
> +#define OAREPORT_REASON_CLK_RATIO (1<<5)
> +
>
> /* For sysctl proc_dointvec_minmax of i915_oa_max_sample_rate
> *
> @@ -303,6 +316,13 @@ static struct i915_oa_format
> hsw_oa_formats[I915_OA_FORMAT_MAX] = {
> [I915_OA_FORMAT_C4_B8] = { 7, 64 },
> };
>
> +static struct i915_oa_format gen8_plus_oa_formats[I915_OA_FORMAT_MAX] = {
> + [I915_OA_FORMAT_A12] = { 0, 64 },
> + [I915_OA_FORMAT_A12_B8_C8] = { 2, 128 },
> + [I915_OA_FORMAT_A32u40_A4u32_B8_C8] = { 5, 256 },
> + [I915_OA_FORMAT_C4_B8] = { 7, 64 },
> +};
> +
> #define SAMPLE_OA_REPORT (1<<0)
>
> /**
> @@ -332,8 +352,20 @@ struct perf_open_properties {
> int oa_period_exponent;
> };
>
> +static u32 gen8_oa_hw_tail_read(struct drm_i915_private *dev_priv)
> +{
> + return I915_READ(GEN8_OATAILPTR) & GEN8_OATAILPTR_MASK;
> +}
> +
> +static u32 gen7_oa_hw_tail_read(struct drm_i915_private *dev_priv)
> +{
> + u32 oastatus1 = I915_READ(GEN7_OASTATUS1);
> +
> + return oastatus1 & GEN7_OASTATUS1_TAIL_MASK;
> +}
> +
> /**
> - * gen7_oa_buffer_check_unlocked - check for data and update tail ptr state
> + * oa_buffer_check_unlocked - check for data and update tail ptr state
> * @dev_priv: i915 device instance
> *
> * This is either called via fops (for blocking reads in user ctx) or the
> poll
> @@ -356,12 +388,11 @@ struct perf_open_properties {
> *
> * Returns: %true if the OA buffer contains data, else %false
> */
> -static bool gen7_oa_buffer_check_unlocked(struct drm_i915_private *dev_priv)
> +static bool oa_buffer_check_unlocked(struct drm_i915_private *dev_priv)
> {
> int report_size = dev_priv->perf.oa.oa_buffer.format_size;
> unsigned long flags;
> unsigned int aged_idx;
> - u32 oastatus1;
> u32 head, hw_tail, aged_tail, aging_tail;
> u64 now;
>
> @@ -381,8 +412,7 @@ static bool gen7_oa_buffer_check_unlocked(struct
> drm_i915_private *dev_priv)
> aged_tail = dev_priv->perf.oa.oa_buffer.tails[aged_idx].offset;
> aging_tail = dev_priv->perf.oa.oa_buffer.tails[!aged_idx].offset;
>
> - oastatus1 = I915_READ(GEN7_OASTATUS1);
> - hw_tail = oastatus1 & GEN7_OASTATUS1_TAIL_MASK;
> + hw_tail = dev_priv->perf.oa.ops.oa_hw_tail_read(dev_priv);
>
> /* The tail pointer increases in 64 byte increments,
> * not in report_size steps...
> @@ -404,6 +434,7 @@ static bool gen7_oa_buffer_check_unlocked(struct
> drm_i915_private *dev_priv)
> if (aging_tail != INVALID_TAIL_PTR &&
> ((now - dev_priv->perf.oa.oa_buffer.aging_timestamp) >
> OA_TAIL_MARGIN_NSEC)) {
> +
> aged_idx ^= 1;
> dev_priv->perf.oa.oa_buffer.aged_tail_idx = aged_idx;
>
> @@ -553,6 +584,284 @@ static int append_oa_sample(struct i915_perf_stream
> *stream,
> *
> * Returns: 0 on success, negative error code on failure.
> */
> +static int gen8_append_oa_reports(struct i915_perf_stream *stream,
> + char __user *buf,
> + size_t count,
> + size_t *offset)
> +{
> + struct drm_i915_private *dev_priv = stream->dev_priv;
> + int report_size = dev_priv->perf.oa.oa_buffer.format_size;
> + u8 *oa_buf_base = dev_priv->perf.oa.oa_buffer.vaddr;
> + u32 gtt_offset = i915_ggtt_offset(dev_priv->perf.oa.oa_buffer.vma);
> + u32 mask = (OA_BUFFER_SIZE - 1);
> + size_t start_offset = *offset;
> + unsigned long flags;
> + unsigned int aged_tail_idx;
> + u32 head, tail;
> + u32 taken;
> + int ret = 0;
> +
> + if (WARN_ON(!stream->enabled))
> + return -EIO;
> +
> + spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);
> +
> + head = dev_priv->perf.oa.oa_buffer.head;
> + aged_tail_idx = dev_priv->perf.oa.oa_buffer.aged_tail_idx;
> + tail = dev_priv->perf.oa.oa_buffer.tails[aged_tail_idx].offset;
> +
> + spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);
> +
> + /* An invalid tail pointer here means we're still waiting for the poll
> + * hrtimer callback to give us a pointer
> + */
> + if (tail == INVALID_TAIL_PTR)
> + return -EAGAIN;
> +
> + /* NB: oa_buffer.head/tail include the gtt_offset which we don't want
> + * while indexing relative to oa_buf_base.
> + */
> + head -= gtt_offset;
> + tail -= gtt_offset;
> +
> + /* An out of bounds or misaligned head or tail pointer implies a driver
> + * bug since we validate + align the tail pointers we read from the
> + * hardware and we are in full control of the head pointer which should
> + * only be incremented by multiples of the report size (notably also
> + * all a power of two).
> + */
> + if (WARN_ONCE(head > OA_BUFFER_SIZE || head % report_size ||
> + tail > OA_BUFFER_SIZE || tail % report_size,
> + "Inconsistent OA buffer pointers: head = %u, tail = %u\n",
> + head, tail))
> + return -EIO;
> +
> +
> + for (/* none */;
> + (taken = OA_TAKEN(tail, head));
> + head = (head + report_size) & mask) {
> + u8 *report = oa_buf_base + head;
> + u32 *report32 = (void *)report;
> + u32 ctx_id;
> + u32 reason;
> +
> + /* All the report sizes factor neatly into the buffer
> + * size so we never expect to see a report split
> + * between the beginning and end of the buffer.
> + *
> + * Given the initial alignment check a misalignment
> + * here would imply a driver bug that would result
> + * in an overrun.
> + */
> + if (WARN_ON((OA_BUFFER_SIZE - head) < report_size)) {
> + DRM_ERROR("Spurious OA head ptr: non-integral report
> offset\n");
> + break;
> + }
> +
> + /* The reason field includes flags identifying what
> + * triggered this specific report (mostly timer
> + * triggered or e.g. due to a context switch).
> + *
> + * This field is never expected to be zero so we can
> + * check that the report isn't invalid before copying
> + * it to userspace...
> + */
> + reason = ((report32[0] >> OAREPORT_REASON_SHIFT) &
> + OAREPORT_REASON_MASK);
> + if (reason == 0) {
> + if (__ratelimit(&dev_priv->perf.oa.spurious_report_rs))
> + DRM_NOTE("Skipping spurious, invalid OA
> report\n");
> + continue;
> + }
> +
> + /* XXX: Just keep the lower 21 bits for now since I'm not
> + * entirely sure if the HW touches any of the higher bits in
> + * this field
> + */
> + ctx_id = report32[2] & 0x1fffff;
> +
> + /* Squash whatever is in the CTX_ID field if it's
> + * marked as invalid to be sure we avoid
> + * false-positive, single-context filtering below...
> + */
> + if (!(report32[0] & dev_priv->perf.oa.gen8_valid_ctx_bit))
> + ctx_id = report32[2] = INVALID_CTX_ID;
> +
> + /* NB: For Gen 8 the OA unit no longer supports clock gating
> + * off for a specific context and the kernel can't securely
> + * stop the counters from updating as system-wide / global
> + * values.
> + *
> + * Automatic reports now include a context ID so reports can be
> + * filtered on the cpu but it's not worth trying to
> + * automatically subtract/hide counter progress for other
> + * contexts while filtering since we can't stop userspace
> + * issuing MI_REPORT_PERF_COUNT commands which would still
> + * provide a side-band view of the real values.
> + *
> + * To allow userspace (such as Mesa/GL_INTEL_performance_query)
> + * to normalize counters for a single filtered context then it
> + * needs be forwarded bookend context-switch reports so that it
> + * can track switches in between MI_REPORT_PERF_COUNT commands
> + * and can itself subtract/ignore the progress of counters
> + * associated with other contexts. Note that the hardware
> + * automatically triggers reports when switching to a new
> + * context which are tagged with the ID of the newly active
> + * context. To avoid the complexity (and likely fragility) of
> + * reading ahead while parsing reports to try and minimize
> + * forwarding redundant context switch reports (i.e. between
> + * other, unrelated contexts) we simply elect to forward them
> + * all.
> + *
> + * We don't rely solely on the reason field to identify context
> + * switches since it's not-uncommon for periodic samples to
> + * identify a switch before any 'context switch' report.
> + */
> + if (!dev_priv->perf.oa.exclusive_stream->ctx ||
> + dev_priv->perf.oa.specific_ctx_id == ctx_id ||
> + (dev_priv->perf.oa.oa_buffer.last_ctx_id ==
> + dev_priv->perf.oa.specific_ctx_id) ||
> + reason & OAREPORT_REASON_CTX_SWITCH) {
> +
> + /* While filtering for a single context we avoid
> + * leaking the IDs of other contexts.
> + */
> + if (dev_priv->perf.oa.exclusive_stream->ctx &&
> + dev_priv->perf.oa.specific_ctx_id != ctx_id) {
> + report32[2] = INVALID_CTX_ID;
> + }
> +
> + ret = append_oa_sample(stream, buf, count, offset,
> + report);
> + if (ret)
> + break;
> +
> + dev_priv->perf.oa.oa_buffer.last_ctx_id = ctx_id;
> + }
> +
> + /* The above reason field sanity check is based on
> + * the assumption that the OA buffer is initially
> + * zeroed and we reset the field after copying so the
> + * check is still meaningful once old reports start
> + * being overwritten.
> + */
> + report32[0] = 0;
> + }
> +
> + if (start_offset != *offset) {
> + spin_lock_irqsave(&dev_priv->perf.oa.oa_buffer.ptr_lock, flags);
> +
> + /* We removed the gtt_offset for the copy loop above, indexing
> + * relative to oa_buf_base so put back here...
> + */
> + head += gtt_offset;
> +
> + I915_WRITE(GEN8_OAHEADPTR, head & GEN8_OAHEADPTR_MASK);
> + dev_priv->perf.oa.oa_buffer.head = head;
> +
> + spin_unlock_irqrestore(&dev_priv->perf.oa.oa_buffer.ptr_lock,
> flags);
> + }
> +
> + return ret;
> +}
> +
> +/**
> + * gen8_oa_read - copy status records then buffered OA reports
> + * @stream: An i915-perf stream opened for OA metrics
> + * @buf: destination buffer given by userspace
> + * @count: the number of bytes userspace wants to read
> + * @offset: (inout): the current position for writing into @buf
> + *
> + * Checks OA unit status registers and if necessary appends corresponding
> + * status records for userspace (such as for a buffer full condition) and
> then
> + * initiate appending any buffered OA reports.
> + *
> + * Updates @offset according to the number of bytes successfully copied into
> + * the userspace buffer.
> + *
> + * NB: some data may be successfully copied to the userspace buffer
> + * even if an error is returned, and this is reflected in the
> + * updated @offset.
> + *
> + * Returns: zero on success or a negative error code
> + */
> +static int gen8_oa_read(struct i915_perf_stream *stream,
> + char __user *buf,
> + size_t count,
> + size_t *offset)
> +{
> + struct drm_i915_private *dev_priv = stream->dev_priv;
> + u32 oastatus;
> + int ret;
> +
> + if (WARN_ON(!dev_priv->perf.oa.oa_buffer.vaddr))
> + return -EIO;
> +
> + oastatus = I915_READ(GEN8_OASTATUS);
> +
> + /* We treat OABUFFER_OVERFLOW as a significant error:
> + *
> + * Although theoretically we could handle this more gracefully
> + * sometimes, some Gens don't correctly suppress certain
> + * automatically triggered reports in this condition and so we
> + * have to assume that old reports are now being trampled
> + * over.
> + *
> + * Considering how we don't currently give userspace control
> + * over the OA buffer size and always configure a large 16MB
> + * buffer, then a buffer overflow does anyway likely indicate
> + * that something has gone quite badly wrong.
> + */
> + if (oastatus & GEN8_OASTATUS_OABUFFER_OVERFLOW) {
> + ret = append_oa_status(stream, buf, count, offset,
> + DRM_I915_PERF_RECORD_OA_BUFFER_LOST);
> + if (ret)
> + return ret;
> +
> + DRM_DEBUG("OA buffer overflow (exponent = %d): force restart\n",
> + dev_priv->perf.oa.period_exponent);
> +
> + dev_priv->perf.oa.ops.oa_disable(dev_priv);
> + dev_priv->perf.oa.ops.oa_enable(dev_priv);
> +
> + /* Note: .oa_enable() is expected to re-init the oabuffer
> + * and reset GEN8_OASTATUS for us
> + */
> + oastatus = I915_READ(GEN8_OASTATUS);
> + }
> +
> + if (oastatus & GEN8_OASTATUS_REPORT_LOST) {
> + ret = append_oa_status(stream, buf, count, offset,
> + DRM_I915_PERF_RECORD_OA_REPORT_LOST);
if ret != 0 shouldn't we bail?
> + if (ret == 0) {
> + I915_WRITE(GEN8_OASTATUS,
> + oastatus & ~GEN8_OASTATUS_REPORT_LOST);
> + }
> + }
> +
> + return gen8_append_oa_reports(stream, buf, count, offset);
> +}
<SNIP>
> +/*
> + * From Broadwell PRM, 3D-Media-GPGPU -> Register State Context
> + *
> + * MMIO reads or writes to any of the registers listed in the
> + * “Register State Context image” subsections through HOST/IA
> + * MMIO interface for debug purposes must follow the steps below:
> + *
> + * - SW should set the Force Wakeup bit to prevent GT from entering C6.
> + * - Write 0x2050[31:0] = 0x00010001 (disable sequence).
> + * - Disable IDLE messaging in CS (Write 0x2050[31:0] = 0x00010001).
> + * - BDW: Poll/Wait for register bits of 0x22AC[6:0] turn to 0x30 value.
> + * - SKL+: Poll/Wait for register bits of 0x22A4[6:0] turn to 0x30 value.
> + * - Read/Write to desired MMIO registers.
> + * - Enable IDLE messaging in CS (Write 0x2050[31:0] = 0x00010000).
> + * - Force Wakeup bit should be reset to enable C6 entry.
> + *
> + * XXX: don't nest or overlap calls to this API, it has no ref
> + * counting to track how many entities require the RCS to be
> + * blocked from being idle.
> + */
> +static int gen8_begin_ctx_mmio(struct drm_i915_private *dev_priv)
> +{
> + i915_reg_t fsm_reg = dev_priv->info.gen > 8 ?
INTEL_GEN?
> + GEN9_RCS_FE_FSM2 : GEN6_RCS_PWR_FSM;
> + int ret = 0;
> +
> + /* There's only no active context while idle in execlist mode
> + * (though we shouldn't be using this in any other case)
> + */
So there may not be an active context? What happens if we do the mmio
and there is no active context?
> + if (WARN_ON(!i915.enable_execlists))
> + return -EINVAL;
> +
> + intel_uncore_forcewake_get(dev_priv, FORCEWAKE_RENDER);
> +
> + I915_WRITE(GEN6_RC_SLEEP_PSMI_CONTROL,
> + _MASKED_BIT_ENABLE(GEN6_PSMI_SLEEP_MSG_DISABLE));
> +
> + /* Note: we don't currently have a good handle on the maximum
> + * latency for this wake up so while we only need to hold rcs
> + * busy from process context we at least keep the waiting
> + * interruptible...
> + */
> + ret = wait_for((I915_READ(fsm_reg) & 0x3f) == 0x30, 50);
intel_wait_for_register(dev_priv, fsm_reg, 0x3f, 0x30, 50), and maybe a
DRM_ERROR timeout message?
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