[PATCH 1/2] drm/msm/dsi: add a helper method to compute the dsi byte clk

[Dmitry Baryshkov]

On 28/10/2022 01:22, Abhinav Kumar wrote:
> 
> 
> On 10/27/2022 10:35 AM, Dmitry Baryshkov wrote:
>> On 22/09/2022 03:49, Abhinav Kumar wrote:
>>> Re-arrange the dsi_calc_pclk method to two helpers, one to
>>> compute the DSI byte clk and the other to compute the pclk.
>>>
>>> This makes the separation of the two clean and also allows
>>> clients to compute and use the dsi byte clk separately.
>>>
>>> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
>>> ---
>>>   drivers/gpu/drm/msm/dsi/dsi.h      |  2 ++
>>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 27 +++++++++++++++++++--------
>>>   2 files changed, 21 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/msm/dsi/dsi.h 
>>> b/drivers/gpu/drm/msm/dsi/dsi.h
>>> index 2a96b4fe7839..60ba8e67f550 100644
>>> --- a/drivers/gpu/drm/msm/dsi/dsi.h
>>> +++ b/drivers/gpu/drm/msm/dsi/dsi.h
>>> @@ -118,6 +118,8 @@ int dsi_link_clk_enable_6g(struct msm_dsi_host 
>>> *msm_host);
>>>   int dsi_link_clk_enable_v2(struct msm_dsi_host *msm_host);
>>>   void dsi_link_clk_disable_6g(struct msm_dsi_host *msm_host);
>>>   void dsi_link_clk_disable_v2(struct msm_dsi_host *msm_host);
>>> +unsigned long dsi_byte_clk_get_rate(struct mipi_dsi_host *host, bool 
>>> is_bonded_dsi,
>>> +        const struct drm_display_mode *mode);
>>>   int dsi_tx_buf_alloc_6g(struct msm_dsi_host *msm_host, int size);
>>>   int dsi_tx_buf_alloc_v2(struct msm_dsi_host *msm_host, int size);
>>>   void *dsi_tx_buf_get_6g(struct msm_dsi_host *msm_host);
>>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c 
>>> b/drivers/gpu/drm/msm/dsi/dsi_host.c
>>> index 57a4c0fa614b..32b35d4ac1d3 100644
>>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
>>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
>>> @@ -569,9 +569,8 @@ void dsi_link_clk_disable_v2(struct msm_dsi_host 
>>> *msm_host)
>>>       clk_disable_unprepare(msm_host->byte_clk);
>>>   }
>>> -static unsigned long dsi_get_pclk_rate(struct msm_dsi_host 
>>> *msm_host, bool is_bonded_dsi)
>>> +static unsigned long dsi_get_pclk_rate(const struct drm_display_mode 
>>> *mode, bool is_bonded_dsi)
>>>   {
>>> -    struct drm_display_mode *mode = msm_host->mode;
>>>       unsigned long pclk_rate;
>>>       pclk_rate = mode->clock * 1000;
>>> @@ -588,12 +587,18 @@ static unsigned long dsi_get_pclk_rate(struct 
>>> msm_dsi_host *msm_host, bool is_bo
>>>       return pclk_rate;
>>>   }
>>> -static void dsi_calc_pclk(struct msm_dsi_host *msm_host, bool 
>>> is_bonded_dsi)
>>> +unsigned long dsi_byte_clk_get_rate(struct mipi_dsi_host *host, bool 
>>> is_bonded_dsi,
>>> +        const struct drm_display_mode *mode)
>>>   {
>>> +    struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
>>>       u8 lanes = msm_host->lanes;
>>>       u32 bpp = dsi_get_bpp(msm_host->format);
>>> -    unsigned long pclk_rate = dsi_get_pclk_rate(msm_host, 
>>> is_bonded_dsi);
>>> -    u64 pclk_bpp = (u64)pclk_rate * bpp;
>>> +    unsigned long pclk_rate;
>>> +    u64 pclk_bpp;
>>> +
>>> +    pclk_rate = dsi_get_pclk_rate(mode, is_bonded_dsi);
>>> +
>>> +    pclk_bpp = (u64)pclk_rate * bpp;
>>>       if (lanes == 0) {
>>>           pr_err("%s: forcing mdss_dsi lanes to 1\n", __func__);
>>> @@ -606,8 +611,14 @@ static void dsi_calc_pclk(struct msm_dsi_host 
>>> *msm_host, bool is_bonded_dsi)
>>>       else
>>>           do_div(pclk_bpp, (8 * lanes));
>>> -    msm_host->pixel_clk_rate = pclk_rate;
>>> -    msm_host->byte_clk_rate = pclk_bpp;
>>> +    return pclk_bpp;
>>> +}
>>> +
>>> +static void dsi_calc_pclk(struct msm_dsi_host *msm_host, bool 
>>> is_bonded_dsi)
>>> +{
>>> +    msm_host->pixel_clk_rate = dsi_get_pclk_rate(msm_host->mode, 
>>> is_bonded_dsi);
>>> +    msm_host->byte_clk_rate = dsi_byte_clk_get_rate(&msm_host->base, 
>>> is_bonded_dsi,
>>> +            msm_host->mode);
>>
>> This way you are calling dsi_get_pclk_rate twice(), which is slightly 
>> inefficient. You can call it once (here) and then pass the resulting 
>> pclk_rate as an argument to dsi_byte_clk_get_rate().
> 
> So the goal was to have two independent APIs to calculate byte and pixel 
> clk.
> 
> If we pass the output of one as the input to the other we are making 
> them dependent.
> 
> Thats why i kept it separate.

Calling one function from another clearly points that they are not 
independent. And surely pixel and byte clocks can not be fully 
independent. I see your point about getting only the byte clock. But I 
think it would be easier to explicitly pass the pixel rate rather than 
calculating it again under the hood.

> 
>>
>>>       DBG("pclk=%lu, bclk=%lu", msm_host->pixel_clk_rate,
>>>                   msm_host->byte_clk_rate);
>>> @@ -635,7 +646,7 @@ int dsi_calc_clk_rate_v2(struct msm_dsi_host 
>>> *msm_host, bool is_bonded_dsi)
>>>       dsi_calc_pclk(msm_host, is_bonded_dsi);
>>> -    pclk_bpp = (u64)dsi_get_pclk_rate(msm_host, is_bonded_dsi) * bpp;
>>> +    pclk_bpp = (u64)dsi_get_pclk_rate(msm_host->mode, is_bonded_dsi) 
>>> * bpp;
>>
>> So... We have calculated all rates, stored the pclk_rate in 
>> msm_host->pixel_clk_rate. And now we are going to calculate it again. 
>> As you are touching this line of code, I'd suggest to just use 
>> msm_host->pixel_clk_rate instead of a function call.
> 
> Ack, I will fix this.
> 
>>
>>>       do_div(pclk_bpp, 8);
>>>       msm_host->src_clk_rate = pclk_bpp;
>>

-- 
With best wishes
Dmitry