linux-kernel - Re: [PATCH] drm/stm: ltdc: use crtc_mode_fixup to update adjusted

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Message-ID: <CA+M3ks55brwkvkU_i947Udmi=KM-ORuVB8YHQd7SUDsinAt4OQ@mail.gmail.com>
Date:   Mon, 29 Jan 2018 11:47:05 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Philippe Cornu <philippe.cornu@...com>,
        Yannick Fertre <yannick.fertre@...com>,
        Vincent Abriou <vincent.abriou@...com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Fabien Dessenne <fabien.dessenne@...com>,
        Mickael Reulier <mickael.reulier@...com>,
        Ludovic Barre <ludovic.barre@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>
Subject: Re: [PATCH] drm/stm: ltdc: use crtc_mode_fixup to update
 adjusted_mode clock

2018-01-29 11:43 GMT+01:00 Laurent Pinchart <laurent.pinchart@...asonboard.com>:
> Hi Philippe,
>
> On Thursday, 25 January 2018 18:01:01 EET Philippe Cornu wrote:
>> There is a difference between the panel/bridge requested pixel clock
>> value and the real one due to the hw platform clock preciseness (pll,
>> dividers...). This patch updates the adjusted_mode clock value with
>> the real hw clock value so then attached encoder & connector can use
>> it for precise timing computations.
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
>> ---
>>  drivers/gpu/drm/stm/ltdc.c | 35 +++++++++++++++++++++++++----------
>>  1 file changed, 25 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
>> index b48589343ae1..90b3de516c91 100644
>> --- a/drivers/gpu/drm/stm/ltdc.c
>> +++ b/drivers/gpu/drm/stm/ltdc.c
>> @@ -428,12 +428,35 @@ static void ltdc_crtc_atomic_disable(struct drm_crtc
>> *crtc, reg_set(ldev->regs, LTDC_SRCR, SRCR_IMR);
>>  }
>>
>> +static bool ltdc_crtc_mode_fixup(struct drm_crtc *crtc,
>> +                              const struct drm_display_mode *mode,
>> +                              struct drm_display_mode *adjusted_mode)
>> +{
>> +     struct ltdc_device *ldev = crtc_to_ltdc(crtc);
>> +     int rate = mode->clock * 1000;
>> +
>> +     /*
>> +      * TODO clk_round_rate() does not work yet. When ready, it can
>> +      * be used instead of clk_set_rate() then clk_get_rate().
>> +      */
>
> Why does it fail ? Is it due to the STM clock source implementation ? This
> looks like a big hack, I'd rather see clk_round_rate() being fixed.

We have log the point and we will investigate it asap.

Regards,
Benjamin

>
>> +     clk_disable(ldev->pixel_clk);
>> +     if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
>> +             DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
>> +             return false;
>> +     }
>> +     clk_enable(ldev->pixel_clk);
>> +
>> +     adjusted_mode->clock = clk_get_rate(ldev->pixel_clk) / 1000;
>> +
>> +     return true;
>> +}
>> +
>>  static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
>>  {
>>       struct ltdc_device *ldev = crtc_to_ltdc(crtc);
>>       struct drm_display_mode *mode = &crtc->state->adjusted_mode;
>>       struct videomode vm;
>> -     int rate = mode->clock * 1000;
>>       u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
>>       u32 total_width, total_height;
>>       u32 val;
>> @@ -456,15 +479,6 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc
>> *crtc) total_width = accum_act_w + vm.hfront_porch;
>>       total_height = accum_act_h + vm.vfront_porch;
>>
>> -     clk_disable(ldev->pixel_clk);
>> -
>> -     if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
>> -             DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
>> -             return;
>> -     }
>> -
>> -     clk_enable(ldev->pixel_clk);
>> -
>>       /* Configures the HS, VS, DE and PC polarities. Default Active Low */
>>       val = 0;
>>
>> @@ -528,6 +542,7 @@ static void ltdc_crtc_atomic_flush(struct drm_crtc
>> *crtc, }
>>
>>  static const struct drm_crtc_helper_funcs ltdc_crtc_helper_funcs = {
>> +     .mode_fixup = ltdc_crtc_mode_fixup,
>>       .mode_set_nofb = ltdc_crtc_mode_set_nofb,
>>       .atomic_flush = ltdc_crtc_atomic_flush,
>>       .atomic_enable = ltdc_crtc_atomic_enable,
>
> --
> Regards,
>
> Laurent Pinchart
>