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

[Joel Stanley]

On Mon, 1 Apr 2019 at 14:32, Eddie James <eajames at linux.ibm.com> wrote:
>
>
> On 4/1/19 1:23 AM, Joel Stanley wrote:
> > 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?
> I disabled interrupts before turning the clocks off. That wasn't the
> only issue, so I had to add the delay after turning clocks on in order
> to reliably get the resolution.
> >
> >>   #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.
> Increasing these helped improve stability when changing resolution.

You need to mention why in your commit message.

> >
> >>   #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?
>
> I used the delay from between the reset assert/deassert used in the old
> aspeed_video_reset function.

Is this what aspeed said we needed? What happens when it's less?

>
> >
> >> @@ -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?
>
> In this case the engine has failed to stop streaming, so it's not
> obeying commands via the registers. Only option is to reset the engine.
> It's an error condition.

This would be a good comment to add to the source code.

>
> >
>