> From: Jani Nikula <jani.nik...@linux.intel.com>
> Sent: Tuesday, June 29, 2021 8:06 PM
> To: Patnana, Venkata Sai <venkata.sai.patn...@intel.com>; intel-
> g...@lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH v2 1/2] drm/i915/display/dsc: Add Per
> connector
> debugfs node for DSC BPP enable
>
> On Tue, 29 Jun 2021, venkata.sai.patn...@intel.com wrote:
> > From: Anusha Srivatsa <anusha.sriva...@intel.com>
> >
> > DSC can be supported per DP connector. This patch creates a per
> > connector debugfs node to expose the Input and Compressed BPP.
> >
> > The same node can be used from userspace to force DSC to a certain
> > BPP.
> >
> > force_dsc_bpp is written through this debugfs node to force DSC BPP to
> > all accepted values
>
> This commit message only describes the "what". It's nice and helpful to
> summarize the code changes.
>
> But the key question the commit message must answer is "why". Why are you
> doing this? Why do we need this?
>
> This looks like it complicates code that is already complicated to add a
> debugfs.
> There needs to be a justification if it isn't obvious.
>
> A couple of comments inline.
>
> >
> > Cc: Vandita Kulkarni <vandita.kulka...@intel.com>
> > Cc: Navare Manasi D <manasi.d.nav...@intel.com>
> > Signed-off-by: Anusha Srivatsa <anusha.sriva...@intel.com>
> > Signed-off-by: Patnana Venkata Sai <venkata.sai.patn...@intel.com>
> > ---
> > .../drm/i915/display/intel_display_debugfs.c | 103 +++++++++++++++++-
> > .../drm/i915/display/intel_display_types.h | 1 +
> > 2 files changed, 103 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > index af9e58619667d..6dc223227eeaa 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> > @@ -2389,6 +2389,100 @@ static const struct file_operations
> i915_dsc_fec_support_fops = {
> > .write = i915_dsc_fec_support_write
> > };
> >
> > +static int i915_dsc_bpp_support_show(struct seq_file *m, void *data)
> > +{
> > + struct drm_connector *connector = m->private;
> > + struct drm_device *dev = connector->dev;
> > + struct drm_crtc *crtc;
> > + struct intel_dp *intel_dp;
> > + struct drm_modeset_acquire_ctx ctx;
> > + struct intel_crtc_state *crtc_state = NULL;
> > + int ret = 0;
> > + bool try_again = false;
> > +
> > + drm_modeset_acquire_init(&ctx,
> DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
> > +
> > + do {
> > + try_again = false;
> > + ret = drm_modeset_lock(&dev-
> >mode_config.connection_mutex,
> > + &ctx);
> > + if (ret) {
> > + ret = -EINTR;
> > + break;
> > + }
> > + crtc = connector->state->crtc;
> > + if (connector->status != connector_status_connected || !crtc) {
> > + ret = -ENODEV;
> > + break;
> > + }
> > + ret = drm_modeset_lock(&crtc->mutex, &ctx);
> > + if (ret == -EDEADLK) {
> > + ret = drm_modeset_backoff(&ctx);
> > + if (!ret) {
> > + try_again = true;
> > + continue;
> > + }
> > + break;
> > + } else if (ret) {
> > + break;
> > + }
> > + intel_dp = intel_attached_dp(to_intel_connector(connector));
> > + crtc_state = to_intel_crtc_state(crtc->state);
> > + seq_printf(m, "Input_BPP: %d\n", crtc_state->pipe_bpp);
> > + seq_printf(m, "Compressed_BPP: %d\n",
> > + crtc_state->dsc.compressed_bpp);
> > + } while (try_again);
> > +
> > + drm_modeset_drop_locks(&ctx);
> > + drm_modeset_acquire_fini(&ctx);
> > +
> > + return ret;
>
> Looks like copy-paste from i915_dsc_fec_support_show() which already makes
> me cringe. We can't keep accumulating this kind of code in debugfs.
@Navare, Manasi D, @Kulkarni, Vandita any thoughts ?
>
> > +}
> > +
> > +static ssize_t i915_dsc_bpp_support_write(struct file *file,
> > + const char __user *ubuf,
> > + size_t len, loff_t *offp)
> > +{
> > + int dsc_bpp = 0;
> > + int ret;
> > + struct drm_connector *connector =
> > + ((struct seq_file *)file->private_data)->private;
> > + struct intel_encoder *encoder =
> intel_attached_encoder(to_intel_connector(connector));
> > + struct drm_i915_private *i915 = to_i915(encoder->base.dev);
> > + struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> > +
> > + if (len == 0)
> > + return 0;
> > +
> > + drm_dbg(&i915->drm,
> > + "Copied %zu bytes from user to force BPP\n", len);
>
> Just no. Again, copy-paste from the fec stuff that we shouldn't have to begin
> with.
>
> > +
> > + ret = kstrtoint_from_user(ubuf, len, 0, &dsc_bpp);
> > +
> > + intel_dp->force_dsc_bpp = dsc_bpp;
> > + if (ret < 0)
> > + return ret;
>
> Check the errors before using the data!
>
> Also, how are you prepared for fractional bpp?
>
> > +
> > + *offp += len;
> > + return len;
> > +}
> > +
> > +static int i915_dsc_bpp_support_open(struct inode *inode,
> > + struct file *file)
> > +{
> > + return single_open(file, i915_dsc_bpp_support_show,
> > + inode->i_private);
> > +}
> > +
> > +static const struct file_operations i915_dsc_bpp_support_fops = {
> > + .owner = THIS_MODULE,
> > + .open = i915_dsc_bpp_support_open,
> > + .read = seq_read,
> > + .llseek = seq_lseek,
> > + .release = single_release,
> > + .write = i915_dsc_bpp_support_write
> > +};
> > +
> > /**
> > * intel_connector_debugfs_add - add i915 specific connector debugfs files
> > * @connector: pointer to a registered drm_connector @@ -2427,9
> > +2521,16 @@ int intel_connector_debugfs_add(struct drm_connector
> *connector)
> > connector,
> &i915_hdcp_sink_capability_fops);
> > }
> >
> > - if ((DISPLAY_VER(dev_priv) >= 11 || IS_CANNONLAKE(dev_priv)) &&
> ((connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort &&
> !to_intel_connector(connector)->mst_port) || connector->connector_type ==
> DRM_MODE_CONNECTOR_eDP))
> > + if ((DISPLAY_VER(dev_priv) >= 11 || IS_CANNONLAKE(dev_priv)) &&
> > + ((connector->connector_type ==
> DRM_MODE_CONNECTOR_DisplayPort &&
> > + !to_intel_connector(connector)->mst_port) ||
> > + connector->connector_type == DRM_MODE_CONNECTOR_eDP)) {
> > debugfs_create_file("i915_dsc_fec_support", S_IRUGO, root,
> > connector, &i915_dsc_fec_support_fops);
> > + debugfs_create_file("i915_dsc_bpp_support", S_IRUGO,
> > + root, connector,
> > + &i915_dsc_bpp_support_fops);
> > + }
> >
> > /* Legacy panels doesn't lpsp on any platform */
> > if ((DISPLAY_VER(dev_priv) >= 9 || IS_HASWELL(dev_priv) || diff
> > --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> > b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index d94f361b548b7..19d8d3eefbc27 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -1612,6 +1612,7 @@ struct intel_dp {
> >
> > /* Display stream compression testing */
> > bool force_dsc_en;
> > + int force_dsc_bpp;
> >
> > bool hobl_failed;
> > bool hobl_active;
>
> --
> Jani Nikula, Intel Open Source Graphics Center
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