sdhci can turn off irq up to 200 ms
From: Matthieu CASTET
Date: Wed Jul 01 2009 - 09:38:50 EST
Hi,
sdhci code got tasklets (sdhci_tasklet_card and sdhci_tasklet_finish),
that does :
{
spin_lock_irqsave
if (cond) {
sdhci_reset
sdhci_reset
}
spin_unlock_irqrestore
}
The problem is that sdhci_reset [1] does busy pooling on a register up
to a timeout of 100 ms.
That's not low latency friendly.
On our system, we saw that sdhci_reset take 1 ms. That should be because
we enter in mdelay, even if the hardware clears the bit faster.
I wonder why there is an mdelay(1). Using cpu_relax and
time_is_after_jiffies should make sdhci_reset faster.
Matthieu
[1]
static void sdhci_reset(struct sdhci_host *host, u8 mask)
{
unsigned long timeout;
u32 uninitialized_var(ier);
[...]
sdhci_writeb(host, mask, SDHCI_SOFTWARE_RESET);
if (mask & SDHCI_RESET_ALL)
host->clock = 0;
/* Wait max 100 ms */
timeout = 100;
/* hw clears the bit when it's done */
while (sdhci_readb(host, SDHCI_SOFTWARE_RESET) & mask) {
if (timeout == 0) {
printk(KERN_ERR "%s: Reset 0x%x never completed.\n",
mmc_hostname(host->mmc), (int)mask);
sdhci_dumpregs(host);
return;
}
timeout--;
mdelay(1);
}
[...]
}
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