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

[Dmitry Baryshkov]

On 31/03/2023 01:49, Jessica Zhang wrote:
> 
> 
> 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 at 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.

Please put this nice description into the commit message. It is exactly 
what I was looking for!

BTW: Do you expect to change MSM_DSC_SLICE_PER_PKT later or it will stay 
at "1"? If so, it might be easier to drop it and instead add a comment.

Regarding eol_byte_num, probably the best explanation would be that is 
is a size of a padding rather than a size of a trailer bytes in a line 
(and thus original calculation was incorrect).

> 
>>
>>>       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!

> 
> 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
>>

-- 
With best wishes
Dmitry