linux-kernel - Re: [PATCH] drm: xlnx: call pm_runtime_get

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Date:   Tue, 16 Mar 2021 19:46:45 +0800
From:   "quanyang.wang" <quanyang.wang@...driver.com>
To:     Hyun Kwon <hyun.kwon@...inx.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Michal Simek <michal.simek@...inx.com>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: xlnx: call pm_runtime_get_sync before setting pixel
 clock

Ping.

Any comment on this patch?

Thanks,

Quanyang

On 3/10/21 12:59 PM, quanyang.wang@...driver.com wrote:
> From: Quanyang Wang <quanyang.wang@...driver.com>
>
> The Runtime PM subsystem will force the device "fd4a0000.zynqmp-display"
> to enter suspend state while booting if the following conditions are met:
> - the usage counter is zero (pm_runtime_get_sync hasn't been called yet)
> - no 'active' children (no zynqmp-dp-snd-xx node under dpsub node)
> - no other device in the same power domain (dpdma node has no
> 		"power-domains = <&zynqmp_firmware PD_DP>" property)
>
> So there is a scenario as below:
> 1) DP device enters suspend state   <- call zynqmp_gpd_power_off
> 2) zynqmp_disp_crtc_setup_clock	    <- configurate register VPLL_FRAC_CFG
> 3) pm_runtime_get_sync		    <- call zynqmp_gpd_power_on and clear previous
> 				       VPLL_FRAC_CFG configuration
> 4) clk_prepare_enable(disp->pclk)   <- enable failed since VPLL_FRAC_CFG
> 				       configuration is corrupted
>
>  From above, we can see that pm_runtime_get_sync may clear register
> VPLL_FRAC_CFG configuration and result the failure of clk enabling.
> Putting pm_runtime_get_sync at the very beginning of the function
> zynqmp_disp_crtc_atomic_enable can resolve this issue.
>
> Signed-off-by: Quanyang Wang <quanyang.wang@...driver.com>
> ---
>   drivers/gpu/drm/xlnx/zynqmp_disp.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_disp.c b/drivers/gpu/drm/xlnx/zynqmp_disp.c
> index 148add0ca1d6..909e6c265406 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_disp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_disp.c
> @@ -1445,9 +1445,10 @@ zynqmp_disp_crtc_atomic_enable(struct drm_crtc *crtc,
>   	struct drm_display_mode *adjusted_mode = &crtc->state->adjusted_mode;
>   	int ret, vrefresh;
>   
> +	pm_runtime_get_sync(disp->dev);
> +
>   	zynqmp_disp_crtc_setup_clock(crtc, adjusted_mode);
>   
> -	pm_runtime_get_sync(disp->dev);
>   	ret = clk_prepare_enable(disp->pclk);
>   	if (ret) {
>   		dev_err(disp->dev, "failed to enable a pixel clock\n");