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

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Message-ID: <f62f3676-b931-6c88-9a49-80c17d16f463@quicinc.com>
Date:   Fri, 19 May 2023 16:02:35 -0700
From:   Jessica Zhang <quic_jesszhan@...cinc.com>
To:     Marijn Suijten <marijn.suijten@...ainline.org>
CC:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        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 5/19/2023 2:24 PM, Marijn Suijten wrote:
> On 2023-05-19 14:17:30, 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.
>>
>> 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;
> 
> Same as the comment below, perhaps it is a good idea to clarify in the
> comment here that the original value wa *multiplied by* slice_per_pkt?
> Otherwise this default of 1 is "invisible".

Hi Marijn,

Acked.

> 
> Alternatively we could have a `const slice_per_pkt = 1;` at the top, and
> have the comment (the elaborate one from below) there?

Since the default slice_per_pkt = 1 and there's only 2 places where I 
have to add a clarifying comment, I think having a separate 
slice_per_pkt variable is a bit redundant.

Plus, if support for multiple slice_per_pkt values is added in the 
future, we'd also have to drop this variable anyways.

Thanks,

Jessica Zhang

> 
> - Marijn
> 
>>   
>>   	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) |
>>
>> -- 
>> 2.40.1
>>