linux-kernel - Re: [PATCH v3 5/5] drm/msm/dsi: Remove incorrect references to slice

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Message-ID: <373d74d0-808a-15a9-b800-3dd40c313b85@quicinc.com>
Date:   Mon, 22 May 2023 11:38:43 -0700
From:   Jessica Zhang <quic_jesszhan@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Marijn Suijten <marijn.suijten@...ainline.org>
CC:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 5/5] drm/msm/dsi: Remove incorrect references to
 slice_count



On 5/20/2023 5:32 PM, Dmitry Baryshkov wrote:
> On 20/05/2023 00:17, Jessica Zhang wrote:
>> Currently, slice_count is being used to calculate word count and
>> pkt_per_line. In downstream, these values are calculated using slice per
>> packet, which is not the same as slice_count.
> 
> I'd say the reference to downstream is not correct. We have seen cases 
> where the vendor kernel contained errors. So it should be something like 
> "Instead these values should be calculated using ...."

Hi Dmitry,

Acked.

Thanks,

Jessica Zhang

> 
>>
>> Slice count represents the number of soft slices per interface, and its
>> value will not always match that of slice per packet. For example, it is
>> possible to have cases where there are multiple soft slices per interface
>> but the panel specifies only one slice per packet.
>>
>> Thus, use the default value of one slice per packet and remove 
>> slice_count
>> from the aforementioned calculations.
>>
>> Fixes: 08802f515c3c ("drm/msm/dsi: Add support for DSC configuration")
>> Fixes: bc6b6ff8135c ("drm/msm/dsi: Use DSC slice(s) packet size to 
>> compute word count")
>> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 24 ++++++++++++++----------
>>   1 file changed, 14 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c 
>> b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> index d04f8bbd707d..8c8858ee59ec 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> @@ -866,18 +866,15 @@ static void dsi_update_dsc_timing(struct 
>> msm_dsi_host *msm_host, bool is_cmd_mod
>>        */
>>       slice_per_intf = msm_dsc_get_slices_per_intf(dsc, hdisplay);
>> -    /*
>> -     * If slice_count is greater than slice_per_intf
>> -     * then default to 1. This can happen during partial
>> -     * update.
>> -     */
>> -    if (dsc->slice_count > slice_per_intf)
>> -        dsc->slice_count = 1;
>> -
>>       total_bytes_per_intf = dsc->slice_chunk_size * slice_per_intf;
>>       eol_byte_num = total_bytes_per_intf % 3;
>> -    pkt_per_line = slice_per_intf / dsc->slice_count;
>> +
>> +    /*
>> +     * Default to 1 slice_per_pkt, so pkt_per_line will be equal to
>> +     * slice per intf.
>> +     */
>> +    pkt_per_line = slice_per_intf;
>>       if (is_cmd_mode) /* packet data type */
>>           reg = 
>> DSI_COMMAND_COMPRESSION_MODE_CTRL_STREAM0_DATATYPE(MIPI_DSI_DCS_LONG_WRITE);
>> @@ -1001,7 +998,14 @@ static void dsi_timing_setup(struct msm_dsi_host 
>> *msm_host, bool is_bonded_dsi)
>>           if (!msm_host->dsc)
>>               wc = hdisplay * dsi_get_bpp(msm_host->format) / 8 + 1;
>>           else
>> -            wc = msm_host->dsc->slice_chunk_size * 
>> msm_host->dsc->slice_count + 1;
>> +            /*
>> +             * When DSC is enabled, WC = slice_chunk_size * 
>> slice_per_packet + 1.
>> +             * Currently, the driver only supports default value of 
>> slice_per_packet = 1
>> +             *
>> +             * TODO: Expand mipi_dsi_device struct to hold 
>> slice_per_packet info
>> +             *       and adjust DSC math to account for 
>> slice_per_packet.
>> +             */
>> +            wc = msm_host->dsc->slice_chunk_size + 1;
>>           dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_CTRL,
>>               DSI_CMD_MDP_STREAM0_CTRL_WORD_COUNT(wc) |
>>
> 
> -- 
> With best wishes
> Dmitry
>