A few more items for the glossary, and understanding GPU switching

A few more items for the glossary, and understanding GPU switching

[Yann Dirson]

Hello,

Back to reading some amdgpu code, I stumbled on a few things that probably ought
to be added to the glossary.  Well, to be fair, I actually just had to read the kernel
logs to see most of them, so those likely make sense to explain.

* ATPX (could not find anything about that on the net). "PX" alone seems to be used 
  as a synonym.  Referred to as "ATPX power control", and closely linked to vga_switcheroo.
  This seems to be a preferred alternative to
  BOCO and BACO, but those are only tersely mentioned in the glossary, and could maybe
  use more details.  There also seem to be the notion of "ATPX hybrid" (which apparently
  applies to the RENOIR in my laptop)
* MACO and BAMACO looks similarly related (I may have missed some ;)
* CRAT seems to be known as "Component Resource Attribute Table" ACPI table according
  to various Internet sources (it is listed as "Component Resource Association Table"
  in kfd_crat.h, do we want to adjust this?), but I could not locate any details on this
  table (ACPI 6.5 seems to list it as deprecated, but even 6.4 just gives erroneous
  information, "Links to ACPI-related Documents" in　https://uefi.org/acpi has no info)
  Is it useful to add to the glossary, with some info about its role in the amdgpu context?


Now about the init on my MSI Bravo17 (Renoir APU, Navi10 dGPU)...

What I understand about ATPX is that this is a "PX system", as shown by amdgpu_atpx_detect()
logging:
 amdgpu: vga_switcheroo: detected switching method \_SB_.PCI0.GP17.VGA_.ATPX handle

So amdgpu seems to imply vga_switcheroo is supposed to get initialized at some point, right?
Similarly with another similar-looking log:

 snd_hda_intel 0000:03:00.1: Handle vga_switcheroo audio client

But no other log see vga_switcheroo actually getting enabled (and the debugfs dir does not
appear either, confirming this).

That is, no call to vga_switcheroo_enable() gets done (both would trigger a
"vga_switcheroo: enabled" log).  The 2 call chains from amdgpu would be:

amdgpu_init()
-> amdgpu_register_atpx_handler()
   -> vga_switcheroo_register_handler()

amdgpu_device_init()
-> vga_switcheroo_register_client()
   -> register_client()

Booting with "tp_printk ftrace=function ftrace_filter=vga_switcheroo_register_handler,vga_switcheroo_register_client,vga_switcheroo_ready" it gets obvious vga_switcheroo_register_client() never not gets called.

The answer seems to lie in amdgpu_device_supports_px(), but I'm not sure to get everything straight here:
amdgpu_device_supports_px() is documented as "Returns true if the device is a dGPU with ATPX power control",
but amdgpu_is_atpx_hybrid() it calls seems to take info from a single static struct, so does the quoted
docstring really make sense?  And if an "APTX hybrid" system does not support vga_switcheroo in the end,
couldn't we just avoid any mention of vga_switcheroo in the logs (since it is indeed amdgpu itself sending
the user on that track), or at least just print once that it is not supported and a short reason?

Best regards,
-- 
Yann

Re: A few more items for the glossary, and understanding GPU switching

[Yann Dirson]

Adding to the list:

* ACA, mentionned in debug_mask flags - digging the source shows it seems to be
  "Accelerator Check Architecture", but maybe some additional details could be
  added?
* DPIA (likely for dc-glossary): listed in DC_DEBUG_MASK values, source code
  in several places shows "DisplayPort Input Adapter", but maybe more details would
  be useful here too?  Often associated with DP USB4 tunneling in source code.

Best regards,
-- 
Yann

[PATCH 0/3] Minor documentation updates

[Yann Dirson]

This series fixes a few small things I stumbled upon while reading the
amdgpu doc.

Yann Dirson (3):
  Documentation/amdgpu: fix 'in the amdgfx' formulation
  drm/amdgpu: fix module parameter description
  Documentation/amdgpu: add a few acronyms to glossary

 Documentation/gpu/amdgpu/amdgpu-glossary.rst              | 3 +++
 Documentation/gpu/amdgpu/display/dc-glossary.rst          | 5 ++++-
 Documentation/gpu/amdgpu/display/display-contributing.rst | 2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c                   | 2 +-
 4 files changed, 9 insertions(+), 3 deletions(-)

-- 
2.39.5

[PATCH 1/3] Documentation/amdgpu: fix 'in the amdgfx' formulation

[Yann Dirson]

Signed-off-by: Yann Dirson <ydirson@free.fr>
---
 Documentation/gpu/amdgpu/display/dc-glossary.rst          | 2 +-
 Documentation/gpu/amdgpu/display/display-contributing.rst | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/gpu/amdgpu/display/dc-glossary.rst b/Documentation/gpu/amdgpu/display/dc-glossary.rst
index 7dc034e9e586..3205f80ad471 100644
--- a/Documentation/gpu/amdgpu/display/dc-glossary.rst
+++ b/Documentation/gpu/amdgpu/display/dc-glossary.rst
@@ -5,7 +5,7 @@ DC Glossary
 On this page, we try to keep track of acronyms related to the display
 component. If you do not find what you are looking for, look at the
 'Documentation/gpu/amdgpu/amdgpu-glossary.rst'; if you cannot find it anywhere,
-consider asking in the amdgfx and update this page.
+consider asking in the amd-gfx mailing list and update this page.
 
 .. glossary::
 
diff --git a/Documentation/gpu/amdgpu/display/display-contributing.rst b/Documentation/gpu/amdgpu/display/display-contributing.rst
index 36f3077eee00..eb148065ddc6 100644
--- a/Documentation/gpu/amdgpu/display/display-contributing.rst
+++ b/Documentation/gpu/amdgpu/display/display-contributing.rst
@@ -9,7 +9,7 @@ contribution to the display code, and for that, we say thank you :)
 
 This page summarizes some of the issues you can help with; keep in mind that
 this is a static page, and it is always a good idea to try to reach developers
-in the amdgfx or some of the maintainers. Finally, this page follows the DRM
+in the amd-gfx mailing list or some of the maintainers. Finally, this page follows the DRM
 way of creating a TODO list; for more information, check
 'Documentation/gpu/todo.rst'.
 
-- 
2.39.5

[PATCH 2/3] drm/amdgpu: fix module parameter description

[Yann Dirson]

Signed-off-by: Yann Dirson <ydirson@free.fr>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 4db92e0a60da..f940068caf72 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -885,7 +885,7 @@ module_param_named(dcfeaturemask, amdgpu_dc_feature_mask, uint, 0444);
 
 /**
  * DOC: dcdebugmask (uint)
- * Override display features enabled. See enum DC_DEBUG_MASK in drivers/gpu/drm/amd/include/amd_shared.h.
+ * Debug options enabled. See enum DC_DEBUG_MASK in drivers/gpu/drm/amd/include/amd_shared.h.
  */
 MODULE_PARM_DESC(dcdebugmask, "all debug options disabled (default))");
 module_param_named(dcdebugmask, amdgpu_dc_debug_mask, uint, 0444);
-- 
2.39.5

[PATCH 3/3] Documentation/amdgpu: add a few acronyms to glossary

[Yann Dirson]

Signed-off-by: Yann Dirson <ydirson@free.fr>
---

Notes (patch):
    test patch note

 Documentation/gpu/amdgpu/amdgpu-glossary.rst     | 3 +++
 Documentation/gpu/amdgpu/display/dc-glossary.rst | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/Documentation/gpu/amdgpu/amdgpu-glossary.rst b/Documentation/gpu/amdgpu/amdgpu-glossary.rst
index 30812d9d53c6..ad9e6f0f91ba 100644
--- a/Documentation/gpu/amdgpu/amdgpu-glossary.rst
+++ b/Documentation/gpu/amdgpu/amdgpu-glossary.rst
@@ -12,6 +12,9 @@ we have a dedicated glossary for Display Core at
       The number of CUs that are active on the system.  The number of active
       CUs may be less than SE * SH * CU depending on the board configuration.
 
+    ACA
+      Accelerator Check Architecture
+
     BACO
       Bus Alive, Chip Off
 
diff --git a/Documentation/gpu/amdgpu/display/dc-glossary.rst b/Documentation/gpu/amdgpu/display/dc-glossary.rst
index 3205f80ad471..d6a6ed4e6374 100644
--- a/Documentation/gpu/amdgpu/display/dc-glossary.rst
+++ b/Documentation/gpu/amdgpu/display/dc-glossary.rst
@@ -88,6 +88,9 @@ consider asking in the amd-gfx mailing list and update this page.
     DIO
       Display IO
 
+    DPIA
+      DisplayPort Input Adapter
+
     DPP
       Display Pipes and Planes
 
-- 
2.39.5

Re: A few more items for the glossary, and understanding GPU switching

[Alex Deucher]

On Sat, Jul 19, 2025 at 7:58 PM Yann Dirson <ydirson@free.fr> wrote:
>
> Hello,
>
> Back to reading some amdgpu code, I stumbled on a few things that probably ought
> to be added to the glossary.  Well, to be fair, I actually just had to read the kernel
> logs to see most of them, so those likely make sense to explain.
>
> * ATPX (could not find anything about that on the net). "PX" alone seems to be used
>   as a synonym.  Referred to as "ATPX power control", and closely linked to vga_switcheroo.

ATPX is the name of an ACPI method.  It stands for ATI PowerXpress.
PowerXpress was the marketing name associated with dGPU d3cold when it
was a vendor specific feature.  Eventually this was standardized by
ACPI and there are standard methods for controlling device power in
the ACPI layer.

>   This seems to be a preferred alternative to
>   BOCO and BACO, but those are only tersely mentioned in the glossary, and could maybe
>   use more details.  There also seem to be the notion of "ATPX hybrid" (which apparently
>   applies to the RENOIR in my laptop)

The ATPX method still exists on some laptops with a dGPU, but it no
longer controls the dGPU power.  That is handled via standard ACPI
methods now and has been for a while.  The driver checks the ATPX
method to determine whether it should use ATPX or the standard ACPI
interfaces for power control.

> * MACO and BAMACO looks similarly related (I may have missed some ;)

BOCO/BACO/BAMACO are all names for various low power states GPU can be put into.

B = Bus
M = Memory
C = Chip
A = Active
O = Off

So BOCO would be Bus Off Chip Off.  Basically the entire PCIe device
is powered down.  Since the PCIe device is powered down, it no longer
appears on the PCIe bus.  This is handled by either ATPX or the
standard ACPI d3cold methods.  BACO is Bus Active Chip Off.  In BACO,
the bus interface is still up, but the chip is powered down, so the
device still shows up on the PCIe bus, but most of the chip is powered
down.  BAMACO and BOMACO are similar to BACO and BOCO, but they keep
VRAM powered up so VRAM contents are not lost when the device is
powered down.

> * CRAT seems to be known as "Component Resource Attribute Table" ACPI table according
>   to various Internet sources (it is listed as "Component Resource Association Table"
>   in kfd_crat.h, do we want to adjust this?), but I could not locate any details on this
>   table (ACPI 6.5 seems to list it as deprecated, but even 6.4 just gives erroneous
>   information, "Links to ACPI-related Documents" in　https://uefi.org/acpi has no info)
>   Is it useful to add to the glossary, with some info about its role in the amdgpu context?
>

CRAT was an ACPI table which was used for topology information for
APUs for ROCm.  Unfortunately, not all board vendors properly
supported the table, so the driver has a fallback to handle missing
CRAT tables.  It hasn't been used for a long time.

>
> Now about the init on my MSI Bravo17 (Renoir APU, Navi10 dGPU)...
>
> What I understand about ATPX is that this is a "PX system", as shown by amdgpu_atpx_detect()
> logging:
>  amdgpu: vga_switcheroo: detected switching method \_SB_.PCI0.GP17.VGA_.ATPX handle
>
> So amdgpu seems to imply vga_switcheroo is supposed to get initialized at some point, right?

IIRC, the switcheroo code looks for certain ACPI methods on its own as well.

> Similarly with another similar-looking log:
>
>  snd_hda_intel 0000:03:00.1: Handle vga_switcheroo audio client
>
> But no other log see vga_switcheroo actually getting enabled (and the debugfs dir does not
> appear either, confirming this).
>
> That is, no call to vga_switcheroo_enable() gets done (both would trigger a
> "vga_switcheroo: enabled" log).  The 2 call chains from amdgpu would be:
>
> amdgpu_init()
> -> amdgpu_register_atpx_handler()
>    -> vga_switcheroo_register_handler()
>
> amdgpu_device_init()
> -> vga_switcheroo_register_client()
>    -> register_client()
>
> Booting with "tp_printk ftrace=function ftrace_filter=vga_switcheroo_register_handler,vga_switcheroo_register_client,vga_switcheroo_ready" it gets obvious vga_switcheroo_register_client() never not gets called.
>
> The answer seems to lie in amdgpu_device_supports_px(), but I'm not sure to get everything straight here:
> amdgpu_device_supports_px() is documented as "Returns true if the device is a dGPU with ATPX power control",
> but amdgpu_is_atpx_hybrid() it calls seems to take info from a single static struct, so does the quoted
> docstring really make sense?  And if an "APTX hybrid" system does not support vga_switcheroo in the end,
> couldn't we just avoid any mention of vga_switcheroo in the logs (since it is indeed amdgpu itself sending
> the user on that track), or at least just print once that it is not supported and a short reason?

ATPX was also used for mux switching on laptops which had a display
mux between the APU and the dGPU.  The switcheroo stuff was for
handling that.
The message comes from the audio driver.  I think it just checks for
the presence of ATPX and sets up switcheroo on the audio side. Someone
could improve the logic in the audio driver (and the switcheroo code
as well) to follow what the GPU driver does if you wanted to avoid
those messages.

>
> Best regards,
> --
> Yann

Re: [PATCH 2/3] drm/amdgpu: fix module parameter description

[Alex Deucher]

Applied the first two patches with some minor changes.

Alex

On Sun, Jul 20, 2025 at 10:14 AM Yann Dirson <ydirson@free.fr> wrote:
>
> Signed-off-by: Yann Dirson <ydirson@free.fr>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index 4db92e0a60da..f940068caf72 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -885,7 +885,7 @@ module_param_named(dcfeaturemask, amdgpu_dc_feature_mask, uint, 0444);
>
>  /**
>   * DOC: dcdebugmask (uint)
> - * Override display features enabled. See enum DC_DEBUG_MASK in drivers/gpu/drm/amd/include/amd_shared.h.
> + * Debug options enabled. See enum DC_DEBUG_MASK in drivers/gpu/drm/amd/include/amd_shared.h.
>   */
>  MODULE_PARM_DESC(dcdebugmask, "all debug options disabled (default))");
>  module_param_named(dcdebugmask, amdgpu_dc_debug_mask, uint, 0444);
> --
> 2.39.5
>

Re: [PATCH 3/3] Documentation/amdgpu: add a few acronyms to glossary

[Alex Deucher]

On Sun, Jul 20, 2025 at 10:23 AM Yann Dirson <ydirson@free.fr> wrote:
>
> Signed-off-by: Yann Dirson <ydirson@free.fr>
> ---
>
> Notes (patch):
>     test patch note
>
>  Documentation/gpu/amdgpu/amdgpu-glossary.rst     | 3 +++
>  Documentation/gpu/amdgpu/display/dc-glossary.rst | 3 +++
>  2 files changed, 6 insertions(+)
>
> diff --git a/Documentation/gpu/amdgpu/amdgpu-glossary.rst b/Documentation/gpu/amdgpu/amdgpu-glossary.rst
> index 30812d9d53c6..ad9e6f0f91ba 100644
> --- a/Documentation/gpu/amdgpu/amdgpu-glossary.rst
> +++ b/Documentation/gpu/amdgpu/amdgpu-glossary.rst
> @@ -12,6 +12,9 @@ we have a dedicated glossary for Display Core at
>        The number of CUs that are active on the system.  The number of active
>        CUs may be less than SE * SH * CU depending on the board configuration.
>
> +    ACA
> +      Accelerator Check Architecture
> +
>      BACO
>        Bus Alive, Chip Off
>
> diff --git a/Documentation/gpu/amdgpu/display/dc-glossary.rst b/Documentation/gpu/amdgpu/display/dc-glossary.rst
> index 3205f80ad471..d6a6ed4e6374 100644
> --- a/Documentation/gpu/amdgpu/display/dc-glossary.rst
> +++ b/Documentation/gpu/amdgpu/display/dc-glossary.rst
> @@ -88,6 +88,9 @@ consider asking in the amd-gfx mailing list and update this page.
>      DIO
>        Display IO
>
> +    DPIA
> +      DisplayPort Input Adapter
> +

Harry, Leo,

Is that the correct expansion of the acronym?

Alex


>      DPP
>        Display Pipes and Planes
>
> --
> 2.39.5
>

Re: [PATCH 3/3] Documentation/amdgpu: add a few acronyms to glossary

[Harry Wentland]

On 2025-07-28 13:18, Alex Deucher wrote:
> On Sun, Jul 20, 2025 at 10:23 AM Yann Dirson <ydirson@free.fr> wrote:
>>
>> Signed-off-by: Yann Dirson <ydirson@free.fr>
>> ---
>>
>> Notes (patch):
>>     test patch note
>>
>>  Documentation/gpu/amdgpu/amdgpu-glossary.rst     | 3 +++
>>  Documentation/gpu/amdgpu/display/dc-glossary.rst | 3 +++
>>  2 files changed, 6 insertions(+)
>>
>> diff --git a/Documentation/gpu/amdgpu/amdgpu-glossary.rst b/Documentation/gpu/amdgpu/amdgpu-glossary.rst
>> index 30812d9d53c6..ad9e6f0f91ba 100644
>> --- a/Documentation/gpu/amdgpu/amdgpu-glossary.rst
>> +++ b/Documentation/gpu/amdgpu/amdgpu-glossary.rst
>> @@ -12,6 +12,9 @@ we have a dedicated glossary for Display Core at
>>        The number of CUs that are active on the system.  The number of active
>>        CUs may be less than SE * SH * CU depending on the board configuration.
>>
>> +    ACA
>> +      Accelerator Check Architecture
>> +
>>      BACO
>>        Bus Alive, Chip Off
>>
>> diff --git a/Documentation/gpu/amdgpu/display/dc-glossary.rst b/Documentation/gpu/amdgpu/display/dc-glossary.rst
>> index 3205f80ad471..d6a6ed4e6374 100644
>> --- a/Documentation/gpu/amdgpu/display/dc-glossary.rst
>> +++ b/Documentation/gpu/amdgpu/display/dc-glossary.rst
>> @@ -88,6 +88,9 @@ consider asking in the amd-gfx mailing list and update this page.
>>      DIO
>>        Display IO
>>
>> +    DPIA
>> +      DisplayPort Input Adapter
>> +
> 
> Harry, Leo,
> 
> Is that the correct expansion of the acronym?
> 

Yes, as far as I know.

Harry

> Alex
> 
> 
>>      DPP
>>        Display Pipes and Planes
>>
>> --
>> 2.39.5
>>