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

[Michel Dänzer]

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?


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer