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Message-ID: <f1bc6b02-0761-c3c0-d629-7b8f97bef8d7@amd.com>
Date: Tue, 4 Aug 2020 12:35:45 -0400
From: "Kazlauskas, Nicholas" <nicholas.kazlauskas@....com>
To: Alexander Monakov <amonakov@...ras.ru>
Cc: amd-gfx@...ts.freedesktop.org,
Alex Deucher <alexander.deucher@....com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: use correct scale for actual_brightness
On 2020-08-04 12:28 p.m., Alexander Monakov wrote:
>
>
> On Tue, 4 Aug 2020, Kazlauskas, Nicholas wrote:
>
>> This is a cleaner change the other proposed patch since it doesn't need to
>
> Can you give a URL to the other patch please?
Sorry, replied to the wrong email by accident here.
The other change was modifying the max_brightness range and rescaling
internal min/max defaults.
I don't think it was sent out to the list yet.
Regards,
Nicholas Kazlauskas
>
>> modify the exist conversion functions but I'd be worried about broken
>> userspace relying on 0-255 as the only acceptable range.
>
> Not sure what you mean by this. Userspace simply reads the maximum value from
> max_brightness sysfs file. On other gpu/firmware combinations it can be 7 or 9
> for example, it just happens to be 255 with modern amdgpu. Minimum value is
> always zero.
>
> Value seen in max_brightness remains 255 with this patch, so as far as userspace
> is concerned nothing is changed apart from value given by actual_brightness file.
>
> Alexander
>
>>
>> Not an expert on existing implementations to point out a specific one though.
>>
>> Regards,
>> Nicholas Kazlauskas
>>
>> On 2020-08-03 4:02 p.m., Alexander Monakov wrote:
>>> Documentation for sysfs backlight level interface requires that
>>> values in both 'brightness' and 'actual_brightness' files are
>>> interpreted to be in range from 0 to the value given in the
>>> 'max_brightness' file.
>>>
>>> With amdgpu, max_brightness gives 255, and values written by the user
>>> into 'brightness' are internally rescaled to a wider range. However,
>>> reading from 'actual_brightness' gives the raw register value without
>>> inverse rescaling. This causes issues for various userspace tools such
>>> as PowerTop and systemd that expect the value to be in the correct
>>> range.
>>>
>>> Introduce a helper to retrieve internal backlight range. Extend the
>>> existing 'convert_brightness' function to handle conversion in both
>>> directions.
>>>
>>> Bug: https://bugzilla.kernel.org/show_bug.cgi?id=203905
>>> Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1242
>>> Cc: Alex Deucher <alexander.deucher@....com>
>>> Signed-off-by: Alexander Monakov <amonakov@...ras.ru>
>>> ---
>>> .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 73 ++++++++-----------
>>> 1 file changed, 32 insertions(+), 41 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 710edc70e37e..03e21e7b7917 100644
>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> @@ -2881,51 +2881,42 @@ static int set_backlight_via_aux(struct dc_link
>>> *link, uint32_t brightness)
>>> return rc ? 0 : 1;
>>> }
>>> -static u32 convert_brightness(const struct amdgpu_dm_backlight_caps
>>> *caps,
>>> - const uint32_t user_brightness)
>>> +static int get_brightness_range(const struct amdgpu_dm_backlight_caps
>>> *caps,
>>> + unsigned *min, unsigned *max)
>>> {
>>> - u32 min, max, conversion_pace;
>>> - u32 brightness = user_brightness;
>>> -
>>> if (!caps)
>>> - goto out;
>>> + return 0;
>>> - if (!caps->aux_support) {
>>> - max = caps->max_input_signal;
>>> - min = caps->min_input_signal;
>>> - /*
>>> - * The brightness input is in the range 0-255
>>> - * It needs to be rescaled to be between the
>>> - * requested min and max input signal
>>> - * It also needs to be scaled up by 0x101 to
>>> - * match the DC interface which has a range of
>>> - * 0 to 0xffff
>>> - */
>>> - conversion_pace = 0x101;
>>> - brightness =
>>> - user_brightness
>>> - * conversion_pace
>>> - * (max - min)
>>> - / AMDGPU_MAX_BL_LEVEL
>>> - + min * conversion_pace;
>>> + if (caps->aux_support) {
>>> + // Firmware limits are in nits, DC API wants millinits.
>>> + *max = 1000 * caps->aux_max_input_signal;
>>> + *min = 1000 * caps->aux_min_input_signal;
>>> } else {
>>> - /* TODO
>>> - * We are doing a linear interpolation here, which is OK but
>>> - * does not provide the optimal result. We probably want
>>> - * something close to the Perceptual Quantizer (PQ) curve.
>>> - */
>>> - max = caps->aux_max_input_signal;
>>> - min = caps->aux_min_input_signal;
>>> -
>>> - brightness = (AMDGPU_MAX_BL_LEVEL - user_brightness) * min
>>> - + user_brightness * max;
>>> - // Multiple the value by 1000 since we use millinits
>>> - brightness *= 1000;
>>> - brightness = DIV_ROUND_CLOSEST(brightness,
>>> AMDGPU_MAX_BL_LEVEL);
>>> + // Firmware limits are 8-bit, PWM control is 16-bit.
>>> + *max = 0x101 * caps->max_input_signal;
>>> + *min = 0x101 * caps->min_input_signal;
>>> }
>>> + return 1;
>>> +}
>>> -out:
>>> - return brightness;
>>> +static u32 convert_brightness(const struct amdgpu_dm_backlight_caps *caps,
>>> + const uint32_t brightness, int from_user)
>>> +{
>>> + unsigned min, max;
>>> +
>>> + if (!get_brightness_range(caps, &min, &max))
>>> + return brightness;
>>> +
>>> + if (from_user)
>>> + // Rescale 0..255 to min..max
>>> + return min + DIV_ROUND_CLOSEST((max - min) * brightness,
>>> + AMDGPU_MAX_BL_LEVEL);
>>> +
>>> + if (brightness < min)
>>> + return 0;
>>> + // Rescale min..max to 0..255
>>> + return DIV_ROUND_CLOSEST(AMDGPU_MAX_BL_LEVEL * (brightness - min),
>>> + max - min);
>>> }
>>> static int amdgpu_dm_backlight_update_status(struct backlight_device
>>> *bd)
>>> @@ -2941,7 +2932,7 @@ static int amdgpu_dm_backlight_update_status(struct
>>> backlight_device *bd)
>>> link = (struct dc_link *)dm->backlight_link;
>>> - brightness = convert_brightness(&caps, bd->props.brightness);
>>> + brightness = convert_brightness(&caps, bd->props.brightness, 1);
>>> // Change brightness based on AUX property
>>> if (caps.aux_support)
>>> return set_backlight_via_aux(link, brightness);
>>> @@ -2958,7 +2949,7 @@ static int amdgpu_dm_backlight_get_brightness(struct
>>> backlight_device *bd)
>>> if (ret == DC_ERROR_UNEXPECTED)
>>> return bd->props.brightness;
>>> - return ret;
>>> + return convert_brightness(&dm->backlight_caps, ret, 0);
>>> }
>>> static const struct backlight_ops amdgpu_dm_backlight_ops = {
>>>
>>> base-commit: bcf876870b95592b52519ed4aafcf9d95999bc9c
>>>
>>
>>
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