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

[Leo Li]

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'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.

Leo

> 
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