On 08/01/2020 22:52, Nicolas Boichat wrote:
On Wed, Jan 8, 2020 at 9:23 PM Mark Brown <broonie@xxxxxxxxxx> wrote:
On Wed, Jan 08, 2020 at 01:23:34PM +0800, Nicolas Boichat wrote:
Some GPUs, namely, the bifrost/g72 part on MT8183, have a second
regulator for their SRAM, let's add support for that.
+ pfdev->regulator_sram = devm_regulator_get_optional(pfdev->dev, "sram");
+ if (IS_ERR(pfdev->regulator_sram)) {
This supply is required for the devices that need it so I'd therefore
expect the driver to request the supply non-optionally based on the
compatible string rather than just hoping that a missing regulator isn't
important.
That'd be a bit awkward to match, though... Currently all bifrost
share the same compatible "arm,mali-bifrost", and it'd seem
weird/wrong to match "mediatek,mt8183-mali" in this driver? I have no
idea if any other Mali implementation will require a second regulator,
but with the MT8183 we do need it, see below.
Though I do have to wonder given the lack of any active
management of the supply if this is *really* part of the GPU or if it's
more of a SoC thing, it's not clear what exactly adding this code is
achieving.
Well if devfreq was working (see patch 7
https://patchwork.kernel.org/patch/11322851/ for a partial
implementation), it would adjust both mali and sram regulators, see
the OPP table in patch 2
(https://patchwork.kernel.org/patch/11322825/): SRAM voltage needs to
be increased for frequencies >=698Mhz.
Now if you have some better idea how to implement this, I'm all ears!
I'm not sure if it's better, but could we just encode the list of regulators into device tree. I'm a bit worried about special casing an "sram" regulator given that other platforms might have a similar situation but call the second regulator a different name.
Steve
Thanks.
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