[PATCH dev-5.0 v2 1/5] media: platform: Aspeed: Remove use of reset line

[Joel Stanley]

On Fri, 29 Mar 2019 at 21:15, Eddie James <eajames at linux.ibm.com> wrote:
>
> The reset line is toggled by enabling the clocks, so it's not necessary
> to manually toggle the reset as well.

Hi Eddie,

You didn't include a changelog here. You said last week that without
the extra reset line toggle you would get interrupt storms. Can you
fill us in on what changed?

>  #define INVALID_RESOLUTION_DELAY       msecs_to_jiffies(250)
> -#define RESOLUTION_CHANGE_DELAY                msecs_to_jiffies(500)
> -#define MODE_DETECT_TIMEOUT            msecs_to_jiffies(500)
> -#define STOP_TIMEOUT                   msecs_to_jiffies(1000)
> +#define RESOLUTION_CHANGE_DELAY                msecs_to_jiffies(750)
> +#define MODE_DETECT_TIMEOUT            msecs_to_jiffies(1000)
> +#define STOP_TIMEOUT                   msecs_to_jiffies(1500)

These numbers changed but you didn't mention why.

>  #define DIRECT_FETCH_THRESHOLD         0x0c0000 /* 1024 * 768 */
>
>  #define VE_MAX_SRC_BUFFER_SIZE         0x8ca000 /* 1920 * 1200, 32bpp */
> @@ -208,7 +207,6 @@ struct aspeed_video {
>         void __iomem *base;
>         struct clk *eclk;
>         struct clk *vclk;
> -       struct reset_control *rst;
>
>         struct device *dev;
>         struct v4l2_ctrl_handler ctrl_handler;
> @@ -483,19 +481,10 @@ static void aspeed_video_enable_mode_detect(struct aspeed_video *video)
>         aspeed_video_update(video, VE_SEQ_CTRL, 0, VE_SEQ_CTRL_TRIG_MODE_DET);
>  }
>
> -static void aspeed_video_reset(struct aspeed_video *video)
> -{
> -       /* Reset the engine */
> -       reset_control_assert(video->rst);
> -
> -       /* Don't usleep here; function may be called in interrupt context */
> -       udelay(100);
> -       reset_control_deassert(video->rst);
> -}
> -
>  static void aspeed_video_off(struct aspeed_video *video)
>  {

> -       aspeed_video_reset(video);
> +       /*
> +        * Delay (and don't sleep in case in interrupt context) to let the
> +        * clocks stabilize. Without this, mode detection sometimes fails.
> +        * Possibly the registers don't update too soon after clocks are
> +        * enabled.
> +        */
> +       udelay(100);

How did you get to 100us?

> @@ -1464,7 +1459,9 @@ static void aspeed_video_stop_streaming(struct vb2_queue *q)

> -               aspeed_video_reset(video);
> +               aspeed_video_off(video);
> +               aspeed_video_on(video);
> +

This includes 5.1ms of sleeping in the clock driver's enable path; are
you sure we need to turn clocks off and on again? Can we avoid the
full reset by instead resetting the registers to a specific state?