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Date:   Fri, 14 Apr 2023 08:48:43 -0700
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Subject: Re: [PATCH] drm/msm/dpu: always program dsc active bits
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To:     Marijn Suijten <marijn.suijten@somainline.org>
CC:     Kuogee Hsieh <quic_khsieh@quicinc.com>, <robdclark@gmail.com>,
        <sean@poorly.run>, <swboyd@chromium.org>, <dianders@chromium.org>,
        <vkoul@kernel.org>, <daniel@ffwll.ch>, <airlied@gmail.com>,
        <agross@kernel.org>, <dmitry.baryshkov@linaro.org>,
        <andersson@kernel.org>, <quic_sbillaka@quicinc.com>,
        <freedreno@lists.freedesktop.org>,
        <dri-devel@lists.freedesktop.org>, <linux-arm-msm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
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From:   Abhinav Kumar <quic_abhinavk@quicinc.com>
In-Reply-To: <mfzi535qsjtcznwdvgb7qyzk25rcsrkwozah6ji4thqsj73n3m@asybxllomisg>
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On 4/14/2023 12:35 AM, Marijn Suijten wrote:
> On 2023-04-12 10:33:15, Abhinav Kumar wrote:
> [..]
>>> What happens if a device boots without DSC panel connected?  Will
>>> CTL_DSC_FLUSH be zero and not (unnecessarily, I assume) flush any of the
>>> DSC blocks?  Or could this flush uninitialized state to the block?
>>>
>>
>> If we bootup without DSC panel connected, the kernel's cfg->dsc will be
>> 0 and default register value of CTL_DSC_FLUSH will be 0 so it wont flush
>> any DSC blocks.
> 
> Ack, that makes sense.  However, if I connect a DSC panel, then
> disconnect it (now the register should be non-zero, but cfg->dsc will be
> zero), and then replug a non-DSC panel multiple times, it'll get flushed
> every time because we never clear CTL_DSC_FLUSH after that?
> 

If we remove it after kernel starts, that issue is there even today 
without that change because DSI is not a hot-pluggable display so a 
teardown wont happen when you plug out the panel. How will cfg->dsc be 0 
then? In that case, its not a valid test as there was no indication to 
DRM that display was disconnected so we cannot tear it down.

>> Sure, as I wrote in the other response, we can move this
>> to reset_intf_cfg later when the other pieces are fixed. And leave a
>> FIXME here.
> 
> Kuogee forgot to CC me on this patchs so I did not read/receive that
> side of the email thread.  Will catch up before reviewing v2.
> 
> - Marijn