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

[Dmitry Baryshkov]

On 31/03/2023 04:12, Jessica Zhang wrote:
> 
> 
> On 3/30/2023 5:16 PM, Dmitry Baryshkov wrote:
>> On Fri, 31 Mar 2023 at 03:07, Jessica Zhang 
>> <quic_jesszhan at quicinc.com> wrote:
>>>
>>>
>>>
>>> On 3/30/2023 4:14 PM, Dmitry Baryshkov wrote:
>>>> 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.
>>>
>>> MSM_DSC_SLICE_PER_PKT is the default value for panels that don't specify
>>> a slice_per_pkt value. (Now that I think about it, might be better to
>>> call it MSM_DSC_DEFAULT_SLICE_PER_PKT instead...)
>>
>> Note, there is no slice_per_pkt in drm_dsc_config, so we must come up
>> with another way to pass this data from the panel or to deduce the
>> value in our driver.
> 
> AFAIK we aren't developing on any panels that have a non-default 
> slice-per-packet count right now, so I'm not sure if it would be worth 
> the effort to add this if there's no panel we can validate it on.
> 
> FWIW, downstream reads slice_per_pkt from a custom DT entry [1]

As you might guess, this approach is frowned upon in upstream kernel. 
This info should come from panel (e.g. extend drm_dsc_config or deduce 
the value in msm driver).

> 
> [1] 
> https://android.googlesource.com/kernel/msm-extra/devicetree/+/refs/heads/android-msm-bramble-4.19-android11-qpr1/qcom/dsi-panel-r66451-dsc-fhd-plus-120hz-cmd.dtsi#115
> 
>>
>>>
>>> I don't expect it to change in the future, but it's a little more
>>> readable than just dividing by 1 IMO. If you prefer dropping the macro
>>> and adding a comment, I'm also okay with that.
>>
>> There is no need to divide by 1, the value doesn't change. So I'd
>> probably prefer something like:
>>
>> /* Default to 1 slice per packet */
>> if (panel_slice_per_pkt)
>>      pkt_per_line = slice_per_intf / panel_slice_per_pkt;
>> else
>>      pkt_per_line = slice_per_intf;
>>
>> Or:
>>
>> /* Default to 1 slice per packet */
>> slice_per_pkt = 1;
>> if (panel_slice_per_pkt)
>>      slice_per_pkt = panel_slice_per_pkt;
>> pkt_per_line = slice_per_intf / slice_per_pkt;
> 
> Acked.
> 


-- 
With best wishes
Dmitry