linux-kernel - Re: [PATCH 3/3] drm/msm/dsi: Enable DATABUS

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Message-ID: <ccda5b11-b074-5500-7c0e-ebb4b025d960@quicinc.com>
Date:   Fri, 16 Jun 2023 14:23:11 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jessica Zhang <quic_jesszhan@...cinc.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Marijn Suijten <marijn.suijten@...ainline.org>
CC:     <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] drm/msm/dsi: Enable DATABUS_WIDEN for DSI command
 mode



On 6/14/2023 12:49 AM, Dmitry Baryshkov wrote:
> On 14/06/2023 04:57, Jessica Zhang wrote:
>> DSI 6G v2.5.x+ supports a data-bus widen mode that allows DSI to send
>> 48 bits of compressed data per pclk instead of 24.
>>
>> For all chipsets that support this mode, enable it whenever DSC is
>> enabled as recommend by the hardware programming guide.
>>
>> Only enable this for command mode as we are currently unable to validate
>> it for video mode.
>>
>> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
>> ---
>>
>> Note: The dsi.xml.h changes were generated using the headergen2 script in
>> envytools [1], but the changes to the copyright and rules-ng-ng source 
>> file
>> paths were dropped.
>>
>> [1] https://github.com/freedreno/envytools/
>>
>>   drivers/gpu/drm/msm/dsi/dsi.xml.h  |  1 +
>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 19 ++++++++++++++++++-
>>   2 files changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi.xml.h 
>> b/drivers/gpu/drm/msm/dsi/dsi.xml.h
>> index a4a154601114..2a7d980e12c3 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi.xml.h
>> +++ b/drivers/gpu/drm/msm/dsi/dsi.xml.h
>> @@ -664,6 +664,7 @@ static inline uint32_t 
>> DSI_CMD_MODE_MDP_CTRL2_INPUT_RGB_SWAP(enum dsi_rgb_swap v
>>       return ((val) << DSI_CMD_MODE_MDP_CTRL2_INPUT_RGB_SWAP__SHIFT) & 
>> DSI_CMD_MODE_MDP_CTRL2_INPUT_RGB_SWAP__MASK;
>>   }
>>   #define DSI_CMD_MODE_MDP_CTRL2_BURST_MODE            0x00010000
>> +#define DSI_CMD_MODE_MDP_CTRL2_DATABUS_WIDEN            0x00100000
>>
>>   #define REG_DSI_CMD_MODE_MDP_STREAM2_CTRL            0x000001b8
>>   #define DSI_CMD_MODE_MDP_STREAM2_CTRL_DATA_TYPE__MASK        0x0000003f
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c 
>> b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> index 5d7b4409e4e9..1da5238e7105 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> @@ -927,6 +927,9 @@ static void dsi_timing_setup(struct msm_dsi_host 
>> *msm_host, bool is_bonded_dsi)
>>       u32 hdisplay = mode->hdisplay;
>>       u32 wc;
>>       int ret;
>> +    bool widebus_supported = msm_host->cfg_hnd->major == 
>> MSM_DSI_VER_MAJOR_6G &&
>> +            msm_host->cfg_hnd->minor >= MSM_DSI_6G_VER_MINOR_V2_5_0;
>> +
>>
>>       DBG("");
>>
>> @@ -973,8 +976,15 @@ static void dsi_timing_setup(struct msm_dsi_host 
>> *msm_host, bool is_bonded_dsi)
>>            *
>>            * hdisplay will be divided by 3 here to account for the fact
>>            * that DPU sends 3 bytes per pclk cycle to DSI.
>> +         *
>> +         * If widebus is supported, set DATABUS_WIDEN register and 
>> divide hdisplay by 6
>> +         * instead of 3
> 
> This is useless, it is already obvious from the code below. Instead 
> there should be something like "wide bus extends that to 6 bytes per 
> pclk cycle"
> 
>>            */
>> -        hdisplay = 
>> DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc), 3);
>> +        if (!(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO) && 
>> widebus_supported)
>> +            hdisplay = 
>> DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc), 6);
>> +        else
>> +            hdisplay = 
>> DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc), 3);
>> +
>>           h_total += hdisplay;
>>           ha_end = ha_start + hdisplay;
>>       }
>> @@ -1027,6 +1037,13 @@ static void dsi_timing_setup(struct 
>> msm_dsi_host *msm_host, bool is_bonded_dsi)
>>           dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_TOTAL,
>>               DSI_CMD_MDP_STREAM0_TOTAL_H_TOTAL(hdisplay) |
>>               DSI_CMD_MDP_STREAM0_TOTAL_V_TOTAL(mode->vdisplay));
>> +
>> +        if (msm_host->dsc && widebus_supported) {
>> +            u32 mdp_ctrl2 = dsi_read(msm_host, 
>> REG_DSI_CMD_MODE_MDP_CTRL2);
>> +
>> +            mdp_ctrl2 |= DSI_CMD_MODE_MDP_CTRL2_DATABUS_WIDEN;
>> +            dsi_write(msm_host, REG_DSI_CMD_MODE_MDP_CTRL2, mdp_ctrl2);
> 
> Is widebus applicable only to the CMD mode, or video mode can employ it 
> too?

Video mode can employ it too but like Jessica said in the commit text, 
we dont have a setup to validate this for DSI video mode so it was 
restricted to cmd mode.

We can leave a note here too.

> 
>> +        }
>>       }
>>   }
>>
>>
>> -- 
>> 2.40.1
>>
>