linux-kernel - Re: [PATCH 2/5] drm: atmel-hlcdc: enable clock before configuring timing engine

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Message-ID: <20191210201845.GA24756@ravnborg.org>
Date:   Tue, 10 Dec 2019 21:18:45 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>
Cc:     bbrezillon@...nel.org, airlied@...ux.ie, daniel@...ll.ch,
        nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        ludovic.desroches@...rochip.com, lee.jones@...aro.org,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] drm: atmel-hlcdc: enable clock before configuring
 timing engine

Hi Claudiu.

On Tue, Dec 10, 2019 at 03:24:44PM +0200, Claudiu Beznea wrote:
> Changing pixel clock source without having this clock source enabled
> will block the timing engine and the next operations after (in this case
> setting ATMEL_HLCDC_CFG(5) settings in atmel_hlcdc_crtc_mode_set_nofb()
> will fail). It is recomended (although in datasheet this is not present)
> to actually enabled pixel clock source before doing any changes on timing
> enginge (only SAM9X60 datasheet specifies that the peripheral clock and
> pixel clock must be enabled before using LCD controller).
> 
> Fixes: 1a396789f65a ("drm: add Atmel HLCDC Display Controller support")
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>

We already had a remotely similar fix.
See 262d67e73f9a920a20bd75278761400404a82de0
("drm: atmel-hlcdc: enable sys_clk during initalization.")

In this patch sys_clk is only enabled if we have a fixed_clk.
Maybe we should do this unconditionally in
atmel_hlcdc_dc_load()?

Then we do not need this enable(disable in the mode_set_nofb
implementation.

Have you considered this way to fix it?

	Sam

> ---
>  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> index 5040ed8d0871..721fa88bf71d 100644
> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
> @@ -73,7 +73,11 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
>  	unsigned long prate;
>  	unsigned int mask = ATMEL_HLCDC_CLKDIV_MASK | ATMEL_HLCDC_CLKPOL;
>  	unsigned int cfg = 0;
> -	int div;
> +	int div, ret;
> +
> +	ret = clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
> +	if (ret)
> +		return;
>  
>  	vm.vfront_porch = adj->crtc_vsync_start - adj->crtc_vdisplay;
>  	vm.vback_porch = adj->crtc_vtotal - adj->crtc_vsync_end;
> @@ -147,6 +151,8 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
>  			   ATMEL_HLCDC_VSPSU | ATMEL_HLCDC_VSPHO |
>  			   ATMEL_HLCDC_GUARDTIME_MASK | ATMEL_HLCDC_MODE_MASK,
>  			   cfg);
> +
> +	clk_disable_unprepare(crtc->dc->hlcdc->sys_clk);
>  }
>  
>  static enum drm_mode_status
> -- 
> 2.7.4