linux-kernel - Re: [PATCH] media: aspeed: use reset to replace clk off/on

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Message-ID: <883dd517-7996-8c44-8cea-1c8838b367b6@linux.intel.com>
Date:   Thu, 4 Nov 2021 08:54:13 -0700
From:   Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
To:     Jammy Huang <jammy_huang@...eedtech.com>, eajames@...ux.ibm.com,
        mchehab@...nel.org, joel@....id.au, andrew@...id.au,
        linux-media@...r.kernel.org, openbmc@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: aspeed: use reset to replace clk off/on

Hi Jammy,

On 11/2/2021 10:43 PM, Jammy Huang wrote:
> reset should be more proper than clk off/on to bring HW back to good
> state.
> 
> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
> ---
>   drivers/media/platform/aspeed-video.c | 22 +++++++++++++++++++---
>   1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
> index fea5e4d0927e..10d182139809 100644
> --- a/drivers/media/platform/aspeed-video.c
> +++ b/drivers/media/platform/aspeed-video.c
> @@ -23,6 +23,7 @@
>   #include <linux/workqueue.h>
>   #include <linux/debugfs.h>
>   #include <linux/ktime.h>
> +#include <linux/reset.h>
>   #include <media/v4l2-ctrls.h>
>   #include <media/v4l2-dev.h>
>   #include <media/v4l2-device.h>
> @@ -220,6 +221,7 @@ struct aspeed_video {
>   	void __iomem *base;
>   	struct clk *eclk;
>   	struct clk *vclk;
> +	struct reset_control *reset;
>   
>   	struct device *dev;
>   	struct v4l2_ctrl_handler ctrl_handler;
> @@ -554,6 +556,13 @@ static void aspeed_video_on(struct aspeed_video *video)
>   	set_bit(VIDEO_CLOCKS_ON, &video->flags);
>   }
>   
> +static void aspeed_video_reset(struct aspeed_video *v)
> +{
> +	reset_control_assert(v->reset);
> +	udelay(100);
> +	reset_control_deassert(v->reset);
> +}
> +
>   static void aspeed_video_bufs_done(struct aspeed_video *video,
>   				   enum vb2_buffer_state state)
>   {
> @@ -574,7 +583,9 @@ static void aspeed_video_irq_res_change(struct aspeed_video *video, ulong delay)
>   	set_bit(VIDEO_RES_CHANGE, &video->flags);
>   	clear_bit(VIDEO_FRAME_INPRG, &video->flags);
>   
> -	aspeed_video_off(video);
> +	aspeed_video_write(video, VE_INTERRUPT_CTRL, 0);
> +	aspeed_video_write(video, VE_INTERRUPT_STATUS, 0xffffffff);
> +	aspeed_video_reset(video);
>   	aspeed_video_bufs_done(video, VB2_BUF_STATE_ERROR);
>   
>   	schedule_delayed_work(&video->res_work, delay);
> @@ -1507,8 +1518,7 @@ static void aspeed_video_stop_streaming(struct vb2_queue *q)
>   		 * Need to force stop any DMA and try and get HW into a good
>   		 * state for future calls to start streaming again.
>   		 */
> -		aspeed_video_off(video);
> -		aspeed_video_on(video);
> +		aspeed_video_reset(video);

You can find the ECLK configuration in 'clk-aspeed.c' or in
'clk-ast2600.c' that it's coupled with the video engine reset (SCU04[6]
for AST2500 / SCU040[6] for AST2600). It means that if we call 
clk_disable() and clk_enable() through aspeed_video_off() and
aspeed_video_on(), the video engine reset will be implicitly asserted
and de-asserted by the clock driver so the reset mechanism is already in
the existing code.

Thanks,
Jae

>   		aspeed_video_init_regs(video);
>   
> @@ -1715,6 +1725,12 @@ static int aspeed_video_init(struct aspeed_video *video)
>   		return rc;
>   	}
>   
> +	video->reset = devm_reset_control_get(dev, NULL);
> +	if (IS_ERR(video->reset)) {
> +		dev_err(dev, "Unable to get reset\n");
> +		return PTR_ERR(video->reset);
> +	}
> +
>   	video->eclk = devm_clk_get(dev, "eclk");
>   	if (IS_ERR(video->eclk)) {
>   		dev_err(dev, "Unable to get ECLK\n");
>