Messages in this thread | | | Date | Tue, 29 Aug 2023 09:55:38 +0530 | Subject | Re: [PATCH 1/2] irqchip/qcom-pdc: don't read version register if it is not available | From | "Maulik Shah (mkshah)" <> |
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Hi,
On 8/28/2023 3:48 PM, Dmitry Baryshkov wrote: > On Mon, 28 Aug 2023 at 13:04, Marc Zyngier <maz@kernel.org> wrote: >> On Mon, 28 Aug 2023 10:46:10 +0100, >> Dmitry Baryshkov <dmitry.baryshkov@linaro.org> wrote: >>> On Mon, 28 Aug 2023 at 12:36, Maulik Shah (mkshah) >>> <quic_mkshah@quicinc.com> wrote: >>>> Hi Dmitry, >>>> >>>> This patch may be useful if there was a case where some PDCs don't have >>>> version register populated/available, >>>> In all PDC versions, version register is always available but due to reg >>>> size not good enough in device tree for SM8150 it failed to read. >>>> >>>> reg size in device node must be expanded if its too small to access all >>>> registers and i think >>>> additional check in driver to check if size is good enough would not be >>>> of much use. >>> Unfortunately, it doesn't work this way. DT files are ABI. Even if we >>> change the DT, the kernel should continue working with the older >>> version. >>> Thus, we have to add such bandaid code, which will keep the kernel >>> from crashing if old DT was used. >> You're missing the point: all existing PDC HW have version register. >> The fact that the DT is crap doesn't invalidate this simple fact. It >> is thus perfectly possible for the driver to *ignore* the crap and do >> the right thing by expanding the size of the mapping, rather than >> falling back to the non-versioned code. > Ah. Interesting idea. If that's the overall consensus I can send v2 > doing this. Not sure what is better though. if expanding register size and reading version register looks too hacky the other way is to have "qcom,pdc-v3.2" compatible for newer targets post which don't need to read version register to figure out as the compatible string is enough to tell if v3.2 HW behavior needs to apply.
I am ok with either approach but biased towards using version register rather than compatibles.
Thanks, Maulik >> There is definitely precedents for this sort of behaviour, such as the >> ARM GICv2 probe code.
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