Re: [PATCH RFT 10/14] drm/msm/a6xx: Stop tracking macrotile_mode (again)

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 5/8/25 8:33 PM, Connor Abbott wrote:
> On Thu, May 8, 2025 at 2:14 PM Konrad Dybcio <konradybcio@kernel.org> wrote:
>>
>> From: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
>>
>> SC8180X (A680) and SA8775P (A663) require a write to that register,
>> while other SKUs are fine with the default value. Don't overwrite it
>> needlessly, requiring the developer to read the value back from
>> hardware just to put it in the driver again, introducing much more room
>> for error.
> 
> I'm not sure I understand that last sentence. The original reason I
> always wrote it was that for host image copy we need to know the value
> of macrotile_mode, so again the value exposed to userspace must match
> what's set in the HW. We can't read the value from the HW and send it
> to userspace, because userspace queries this when creating the
> physical device during device enumeration and we really don't want to
> spuriously turn on the device then. That means the safest thing is to
> always program it, guaranteeing that it always matches. Otherwise we
> just have to hope that the default value matches what we expect it to
> be.
> 
> I know you're copying this from kgsl, but kgsl doesn't expose the
> macrotile_mode to userspace. I expect that HIC was added afterwards
> and only works via hacks there (if it's even supported at all on the
> relevant SoCs).

Alright, I think I'll include it in the common UBWC config (even though
it only concerns the GPU), as IIUC it may differ between platforms
implementing the same GPU SKU

Konrad