[PATCH 04/33] drm/amd/display: Use 4096 lut entries

[Harry Wentland]

On 2018-02-27 11:44 AM, Michel Dänzer wrote:
> On 2018-02-27 05:16 PM, Harry Wentland wrote:
>> On 2018-02-27 11:08 AM, Michel Dänzer wrote:
>>> On 2018-02-27 04:54 PM, Leo Li wrote:
>>>> On 2018-02-27 05:34 AM, Michel Dänzer wrote:
>>>>> On 2018-02-26 09:15 PM, Harry Wentland wrote:
>>>>>> From: "Leo (Sunpeng) Li" <sunpeng.li at amd.com>
>>>>>>
>>>>>> Non-legacy LUT size should reflect hw capability. Change size from 256
>>>>>> to 4096.
>>>>>>
>>>>>> However, X doesn't seem to play with legacy LUTs of such size.
>>>>>> Therefore, check for legacy lut when updating DC states, and update
>>>>>> accordingly.
>>>>>>
>>>>>> v2: Use a macro for the maximum drm LUT value.
>>>>>>
>>>>>> Signed-off-by: Leo (Sunpeng) Li <sunpeng.li at amd.com>
>>>>>> Reviewed-by: Harry Wentland <Harry.Wentland at amd.com>
>>>>>> ---
>>>>>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c  |  2 +-
>>>>>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h  |  4 +-
>>>>>>   .../drm/amd/display/amdgpu_dm/amdgpu_dm_color.c    | 77
>>>>>> ++++++++++++++++------
>>>>>>   3 files changed, 61 insertions(+), 22 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>>> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>>> index bb9405daa087..f782518fc424 100644
>>>>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>>>>> @@ -3228,7 +3228,7 @@ static int amdgpu_dm_crtc_init(struct
>>>>>> amdgpu_display_manager *dm,
>>>>>>       dm->adev->mode_info.crtcs[crtc_index] = acrtc;
>>>>>>       drm_crtc_enable_color_mgmt(&acrtc->base, MAX_COLOR_LUT_ENTRIES,
>>>>>>                      true, MAX_COLOR_LUT_ENTRIES);
>>>>>> -    drm_mode_crtc_set_gamma_size(&acrtc->base, MAX_COLOR_LUT_ENTRIES);
>>>>>> +    drm_mode_crtc_set_gamma_size(&acrtc->base,
>>>>>> MAX_COLOR_LEGACY_LUT_ENTRIES);
>>>>>
>>>>> This means userspace can't set gamma ramps with more than 256 entries,
>>>>> since drm_mode_gamma_set_ioctl returns an error if the sizes don't
>>>>> match. We should just fix userspace which tries to use the wrong size.
>>>>
>>>> It seems X hard-codes 256 entries for the legacy lut, ignoring what the
>>>> kernel requests:
>>>>
>>>> xf86CrtcCreate in xserver/hw/xfree86/modes/xf86Crtc.c (~line 120):
>>>>
>>>> /* Preallocate gamma at a sensible size. */
>>>> crtc->gamma_size = 256;
>>>>
>>>>
>>>> I confirmed this as well via a printk on the user LUT size in
>>>> drm_mode_gamma_set_ioctl (after reverting to 4096 gamma size, of course).
>>>>
>>>> I'm not sure if modifying that line in X will be straightforward.
>>>
>>> It could be overridden by the DDX driver. However, there is the issue of
>>> using an older DDX driver with a newer kernel.
>>>
>>>
>>>> It's worth noting that drm_mode_crtc_set_gamma_size() only sets the legacy
>>>> gamma size. Non-legacy gamma (de/regamma) sizes are reported via a mode
>>>> property, and does not conflict with legacy size. Therefore, reporting a
>>>> different size for legacy shouldn't be an issue, AFAIK; as long as we
>>>> check the DRM lut size and update DC accordingly, which we're doing.
>>>
>>> Makes sense, but it means that gamma will not work for 30-bit colour in
>>> Xorg until the DDX driver uses the new gamma mechanism, which might
>>> require switching to the atomic KMS API as well. Is that okay?
>>>
>>
>> That's still current behavior, so this patch is not changing anything there. We could increase it but how would we deal with old DDX/X that assumes 256? Would it make sense instead to teach X to set the new gamma_lut property?
> 
> Maybe. Can it be used without using the atomic KMS UAPI in general?
> 

Both legacy and atomic KMS can set non-legacy gamma(the new degamma_lut, ctm, and gamma_lut properties on CRTC). Legacy KMS can use DRM_IOCTL_MODE_SETPROPERTY to set these. IGT exercises both atomic and non-atomic KMS code paths to test these properties.

Only legacy KMS sets the legacy gamma property through the DRM_IOCTL_MODE_SETGAMMA IOCTL.

Harry

>