Re: [PATCH RFC 5/5] drm/msm/dsi: Use MSM and DRM DSC helper methods

[Jessica Zhang <quic_jesszhan@quicinc.com>]

On 3/29/2023 4:48 PM, Dmitry Baryshkov wrote:
> On 30/03/2023 02:18, Jessica Zhang wrote:
>> Use MSM and DRM DSC helper methods.
>>
>> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
>> ---
>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 18 ++++++++++++------
>>   1 file changed, 12 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c 
>> b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> index 74d38f90398a..7419fe58a941 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> @@ -31,6 +31,7 @@
>>   #include "msm_kms.h"
>>   #include "msm_gem.h"
>>   #include "phy/dsi_phy.h"
>> +#include "disp/msm_dsc_helper.h"
>>   #define DSI_RESET_TOGGLE_DELAY_MS 20
>> @@ -841,14 +842,14 @@ static void dsi_update_dsc_timing(struct 
>> msm_dsi_host *msm_host, bool is_cmd_mod
>>   {
>>       struct drm_dsc_config *dsc = msm_host->dsc;
>>       u32 reg, reg_ctrl, reg_ctrl2;
>> -    u32 slice_per_intf, total_bytes_per_intf;
>> +    u32 slice_per_intf;
>>       u32 pkt_per_line;
>>       u32 eol_byte_num;
>>       /* first calculate dsc parameters and then program
>>        * compress mode registers
>>        */
>> -    slice_per_intf = DIV_ROUND_UP(hdisplay, dsc->slice_width);
>> +    slice_per_intf = msm_dsc_get_slice_per_intf(dsc, hdisplay);
> 
> This looks good
> 
>>       /*
>>        * If slice_count is greater than slice_per_intf
>> @@ -858,10 +859,10 @@ static void dsi_update_dsc_timing(struct 
>> msm_dsi_host *msm_host, bool is_cmd_mod
>>       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 = msm_dsc_get_eol_byte_num(msm_host->dsc, hdisplay,
>> +            dsi_get_bpp(msm_host->format));
>> -    eol_byte_num = total_bytes_per_intf % 3;
>> -    pkt_per_line = slice_per_intf / dsc->slice_count;
>> +    pkt_per_line = slice_per_intf / MSM_DSC_SLICE_PER_PKT;
> 
> And for these values the result is definitely changed. Separate patch & 
> description please. Just in case, "values per downstream kernel" is not 
> a proper description for such changes.

Hi Dmitry,

Sure, I can put this into a separate patch.

The reason this was changed from slice_count to SLICE_PER_PKT was 
because slice count and slice per packet aren't always equivalent. There 
can be cases where panel configures DSC to have multiple soft slices per 
interface, but the panel only specifies 1 slice per packet.

> 
>>       if (is_cmd_mode) /* packet data type */
>>           reg = 
>> DSI_COMMAND_COMPRESSION_MODE_CTRL_STREAM0_DATATYPE(MIPI_DSI_DCS_LONG_WRITE);
>> @@ -911,6 +912,11 @@ static void dsi_timing_setup(struct msm_dsi_host 
>> *msm_host, bool is_bonded_dsi)
>>       DBG("");
>> +    if (msm_host->mode_flags & MIPI_DSI_MODE_VIDEO)
>> +        /* Default widebus_en to false for now. */
>> +        hdisplay = msm_dsc_get_pclk_per_line(msm_host->dsc, 
>> mode->hdisplay,
>> +                dsi_get_bpp(msm_host->format));
>> +
> 
> This is definitely something new and thus should probably go into a 
> separate patch and be described. Also I'm not sure how does that 
> interact with the hdisplay-related calculations below, under the if(dsc) 
> clause.

After double-checking the math here, I think this part of the change is 
actually wrong. pclk_per_line is essentially doing hdisplay / 3, which 
is a repeat of what's being done in the `if (dsc)` block.

Will replace `hdisplay /= 3` with the pclk_per_line calculation.

Thanks,

Jessica Zhang

> 
>>       /*
>>        * For bonded DSI mode, the current DRM mode has
>>        * the complete width of the panel. Since, the complete
>> @@ -1759,7 +1765,7 @@ static int dsi_populate_dsc_params(struct 
>> msm_dsi_host *msm_host, struct drm_dsc
>>           return ret;
>>       }
>> -    dsc->initial_scale_value = 32;
>> +    dsc->initial_scale_value = 
>> drm_dsc_calculate_initial_scale_value(dsc);
> 
> This is fine, we only support 8bpp where these values match.
> 
>>       dsc->line_buf_depth = dsc->bits_per_component + 1;
>>       return drm_dsc_compute_rc_parameters(dsc);
>>
> 
> -- 
> With best wishes
> Dmitry
>