[PATCH 3/6] staging: drm/imx: add i.MX IPUv3 base driver

On Fri, Sep 14, 2012 at 11:29:06AM +0200, Dirk Behme wrote:

On 12.09.2012 12:31, Sascha Hauer wrote:

quoted

+
+       timeout = jiffies + msecs_to_jiffies(1000);
+       while (ipu_cm_read(ipu, IPU_MEM_RST) & 0x80000000) {
+               if (time_after(jiffies, timeout))
+                       return -ETIME;
+               cpu_relax();
+       }
+
+       mdelay(300);

          ^^^^^^^^^^^^

quoted

+       return 0;
+}

While doing some boot time measurement with i.MX6, we found that the
above mdelay(300) is hurting regarding boot time. On i.MX6 you have
two IPU instances, so in the end you get 600ms additional delay.

Looking at the Freescale code, this function looks like

static int ipu_reset(struct ipu_soc *ipu)
{
int timeout = 1000;

ipu_cm_write(ipu, 0x807FFFFF, IPU_MEM_RST);

while (ipu_cm_read(ipu, IPU_MEM_RST) & 0x80000000) {
 if (!timeout--)
   return -ETIME;
 msleep(1);
}
return 0;
}

So there is a msleep() in the loop but no mdelay() outside. Any idea
why the mdelay() is needed here? Or what could be done regarding
boot time with this?

I remember we had issues on i.MX51 or 53 without it, but I would have to
recheck it.
In any way, I think this should be reworked. The reset takes quite a
long time and it's not nice to block the boot process for so long.
Some asynchronous reset would be nice here.

Sascha

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