On 7/22/2025 8:22 PM, Konrad Dybcio wrote:
> On 7/22/25 3:39 PM, Dmitry Baryshkov wrote:
>> On Sun, Jul 20, 2025 at 05:46:08PM +0530, Akhil P Oommen wrote:
>>> There are some special registers which are accessible even when GX power
>>> domain is collapsed during an IFPC sleep. Accessing these registers
>>> wakes up GPU from power collapse and allow programming these registers
>>> without additional handshake with GMU. This patch adds support for this
>>> special register write sequence.
>>>
>>> Signed-off-by: Akhil P Oommen <akhi...@oss.qualcomm.com>
>>> ---
>>> drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 63
>>> ++++++++++++++++++++++++++++++-
>>> drivers/gpu/drm/msm/adreno/a6xx_gpu.h | 1 +
>>> drivers/gpu/drm/msm/adreno/a6xx_preempt.c | 20 +++++-----
>>> 3 files changed, 73 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>> b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>> index
>>> 491fde0083a202bec7c6b3bca88d0e5a717a6560..8c004fc3abd2896d467a9728b34e99e4ed944dc4
>>> 100644
>>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>>> @@ -16,6 +16,67 @@
>>>
>>> #define GPU_PAS_ID 13
>>>
>>> +static bool fence_status_check(struct msm_gpu *gpu, u32 offset, u32 value,
>>> u32 status, u32 mask)
>>> +{
>>> + /* Success if !writedropped0/1 */
>>> + if (!(status & mask))
>>> + return true;
>>> +
>>> + udelay(10);
>>
>> Why do we need udelay() here? Why can't we use interval setting inside
>> gmu_poll_timeout()?
>
> Similarly here:
>
> [...]
>
>>> + if (!gmu_poll_timeout(gmu, REG_A6XX_GMU_AHB_FENCE_STATUS, status,
>>> + fence_status_check(gpu, offset, value, status, mask),
>>> 0, 1000))
>>> + return 0;
>>> +
>>> + dev_err_ratelimited(gmu->dev, "delay in fenced register write (0x%x)\n",
>>> + offset);
>>> +
>>> + /* Try again for another 1ms before failing */
>>> + gpu_write(gpu, offset, value);
>>> + if (!gmu_poll_timeout(gmu, REG_A6XX_GMU_AHB_FENCE_STATUS, status,
>>> + fence_status_check(gpu, offset, value, status, mask),
>>> 0, 1000))
>>> + return 0;
>>> +
>>> + dev_err_ratelimited(gmu->dev, "fenced register write (0x%x) fail\n",
>>> + offset);
>
> We may want to combine the two, so as not to worry the user too much..
>
> If it's going to fail, I would assume it's going to fail both checks
> (unless e.g. the bus is so congested a single write can't go through
> to a sleepy GPU across 2 miliseconds, but that's another issue)
In case of success, we cannot be sure if the first write went through.
So we should poll separately.
-Akhil.
>
> Konrad
