On 5/14/2024 5:00 PM, Easwar Hariharan wrote:
On 5/14/2024 4:17 PM, Roman Kisel wrote:
On 5/14/2024 3:46 PM, Easwar Hariharan wrote:
On 5/10/2024 10:42 AM, Roman Kisel wrote:
On 5/10/2024 10:04 AM, Easwar Hariharan wrote:
On 5/10/2024 9:05 AM, rom...@linux.microsoft.com wrote:
From: Roman Kisel <rom...@linux.microsoft.com>
Update the driver to support DeviceTree boot as well along with ACPI.
This enables the Virtual Trust Level platforms boot up on ARM64.
Signed-off-by: Roman Kisel <rom...@linux.microsoft.com>
---
arch/arm64/hyperv/mshyperv.c | 34 +++++++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index b1a4de4eee29..208a3bcb9686 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -15,6 +15,9 @@
#include <linux/errno.h>
#include <linux/version.h>
#include <linux/cpuhotplug.h>
+#include <linux/libfdt.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
#include <asm/mshyperv.h>
static bool hyperv_initialized;
@@ -27,6 +30,29 @@ int hv_get_hypervisor_version(union
hv_hypervisor_version_info *info)
return 0;
}
+static bool hyperv_detect_fdt(void)
+{
+#ifdef CONFIG_OF
+ const unsigned long hyp_node = of_get_flat_dt_subnode_by_name(
+ of_get_flat_dt_root(), "hypervisor");
+
+ return (hyp_node != -FDT_ERR_NOTFOUND) &&
+ of_flat_dt_is_compatible(hyp_node, "microsoft,hyperv");
+#else
+ return false;
+#endif
+}
+
+static bool hyperv_detect_acpi(void)
+{
+#ifdef CONFIG_ACPI
+ return !acpi_disabled &&
+ !strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8);
+#else
+ return false;
+#endif
+}
+
Could using IS_ENABLED() allow collapsing these two functions into one
hyperv_detect_fw()?
I am wondering if #ifdef was explicitly chosen to allow for the code to be
compiled in if CONFIG* is defined
v/s IS_ENABLED() only being true if the CONFIG value is true.
In the hyperv_detect_fdt function, the #ifdef has been chosen due to the
functions being declared only when the macro is defined, hence I could not rely
on `if IS_ENABLED()` and the run-time detection. For the compile-time option,
`#if IS_ENABLED()` would convey the intent better, could update with that.
In patch 2/6, just under the diff you have, we already `select
OF_EARLY_FLATTREE if OF`, so the declarations (and definitions)
of the functions being present is already handled, AFAIK. Are we thinking there
may be some weird config where neither OF nor
ACPI is selected? If so, we should set a `depends on ACPI || OF` for config
HYPERV to prevent that.
I don't know if I'm missing something obvious here, so please correct me if I'm
wrong.
I just sent out the v2 of the patch set, and (un?)fortunately missed the change
I had for the #ifdef's in this chunk (to use #if IS_ENABLED() and remove
pre-processor directives from the ACPI-related function).
I am making the point that the change you are suggesting (as I understand) is
this conditional statement
if IS_ENABLED(CONFIG_OF) {
const unsigned long hyp_node = of_get_flat_dt_subnode_by_name(
of_get_flat_dt_root(), "hypervisor");
return (hyp_node != -FDT_ERR_NOTFOUND) &&
of_flat_dt_is_compatible(hyp_node, "microsoft,hyperv");
}
That's right, that's the suggestion I'm making.
and for it to link successfully, one needs of_get_flat_dt_subnode_by_name
defined. From the source code, that needs CONFIG_OF_EARLY_FLATTREE as there is
no stub available when CONFIG_OF_EARLY_FLATTREE is not defined.
We agree that you need of_get_flat_dt_subnode_by_name declared and defined, and
it's not available, stub or otherwise, if CONFIG_OF_EARLY_FLATTREE is not
defined.
In my mind, I believed that either ACPI or OF had to be selected for some sort
of firmware handoff to occur, but I did some experimentation and ended up with
an
x86_64 kernel config that has neither enabled, but nonetheless has
CONFIG_HYPERV enabled. The kernel builds with such a config, whether it's
useful for anything
is another question. ARM64 requires CONFIG_OF so that side of the equation is
clear.
That's where my question above came in: Are we thinking there may be some weird
config where neither OF nor ACPI is selected? I thought that was not a
reasonable
config, thus my prescription to set `depends on ACPI || OF` for config HYPERV.
If there is a use case for an x86_64 kernel that has neither ACPI nor
OpenFirmware/FDT,
but nevertheless sets CONFIG_HYPERV, feel free to ignore this comment thread
entirely.
Thanks for laying out the details so patiently for me! I believe I
understand your concerns better now. In the V2 of the patch series,
Michael Kelly suggested rethinking how the Kconfig change is carried
out. Appears natural to try out what your suggesting alongside with the
Michael's suggestions.
As for your other point, I wouldn't think, too, the system could boot or
be useful without some coordinates of the environment passed via ACPI || DT.
Thanks,
Easwar
--
Thank you,
Roman
