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Date:   Tue, 19 Jul 2022 12:07:16 +0530
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Subject: Re: [Freedreno] [PATCH v2 5/7] arm64: dts: qcom: sc7280: Update gpu
 register list
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To:     Stephen Boyd <swboyd@chromium.org>,
        Doug Anderson <dianders@chromium.org>,
        Taniya Das <quic_tdas@quicinc.com>, <quic_rjendra@quicinc.com>
CC:     <devicetree@vger.kernel.org>, Jonathan Marek <jonathan@marek.ca>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Andy Gross <agross@kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "Bjorn Andersson" <bjorn.andersson@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Rob Clark <robdclark@gmail.com>,
        Matthias Kaehlcke <mka@chromium.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Jordan Crouse <jordan@cosmicpenguin.net>,
        freedreno <freedreno@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <1657346375-1461-1-git-send-email-quic_akhilpo@quicinc.com>
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 <c022538d-c616-8f1a-e1c2-c11b5f0de670@quicinc.com>
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 <CAE-0n52TG3hsytN5nRU7W=S6PffSj8yQDmuicN0-qxoW-jxiZQ@mail.gmail.com>
From:   Akhil P Oommen <quic_akhilpo@quicinc.com>
In-Reply-To: <CAE-0n52TG3hsytN5nRU7W=S6PffSj8yQDmuicN0-qxoW-jxiZQ@mail.gmail.com>
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On 7/19/2022 11:19 AM, Stephen Boyd wrote:
> Quoting Akhil P Oommen (2022-07-18 21:07:05)
>> On 7/14/2022 11:10 AM, Akhil P Oommen wrote:
>>> On 7/12/2022 4:57 AM, Doug Anderson wrote:
>>>> Hi,
>>>>
>>>> On Fri, Jul 8, 2022 at 11:00 PM Akhil P Oommen
>>>> <quic_akhilpo@quicinc.com> wrote:
>>>>> Update gpu register array with gpucc memory region.
>>>>>
>>>>> Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
>>>>> ---
>>>>>
>>>>> (no changes since v1)
>>>>>
>>>>>    arch/arm64/boot/dts/qcom/sc7280.dtsi | 6 ++++--
>>>>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/arch/arm64/boot/dts/qcom/sc7280.dtsi
>>>>> b/arch/arm64/boot/dts/qcom/sc7280.dtsi
>>>>> index e66fc67..defdb25 100644
>>>>> --- a/arch/arm64/boot/dts/qcom/sc7280.dtsi
>>>>> +++ b/arch/arm64/boot/dts/qcom/sc7280.dtsi
>>>>> @@ -2228,10 +2228,12 @@
>>>>>                           compatible = "qcom,adreno-635.0",
>>>>> "qcom,adreno";
>>>>>                           reg = <0 0x03d00000 0 0x40000>,
>>>>>                                 <0 0x03d9e000 0 0x1000>,
>>>>> -                             <0 0x03d61000 0 0x800>;
>>>>> +                             <0 0x03d61000 0 0x800>,
>>>>> +                             <0 0x03d90000 0 0x2000>;
>>>>>                           reg-names = "kgsl_3d0_reg_memory",
>>>>>                                       "cx_mem",
>>>>> -                                   "cx_dbgc";
>>>>> +                                   "cx_dbgc",
>>>>> +                                   "gpucc";
>>>> This doesn't seem right. Shouldn't you be coordinating with the
>>>> existing gpucc instead of reaching into its registers?
>>>>
>>> IIUC, qcom gdsc driver doesn't ensure hardware is collapsed since they
>>> are vote-able switches. Ideally, we should ensure that the hw has
>>> collapsed for gpu recovery because there could be transient votes from
>>> other subsystems like hypervisor using their vote register.
>>>
>>> I am not sure how complex the plumbing to gpucc driver would be to allow
>>> gpu driver to check hw status. OTOH, with this patch, gpu driver does a
>>> read operation on a gpucc register which is in always-on domain. That
>>> means we don't need to vote any resource to access this register.
>>>
>>> Stephen/Rajendra/Taniya, any suggestion?
> Why can't you assert a gpu reset signal with the reset APIs? This series
> seems to jump through a bunch of hoops to get the gdsc and power domain
> to "reset" when I don't know why any of that is necessary. Can't we
> simply assert a reset to the hardware after recovery completes so the
> device is back into a good known POR (power on reset) state?
That is because there is no register interface to reset GPU CX domain. 
The recommended sequence from HW design folks is to collapse both cx and 
gx gdsc to properly reset gpu/gmu.

-Akhil.