On Thursday, 3 of July 2008, Zhang Rui wrote:
> During S3 resume, AHCI driver sleeps 1 second to wait for the HBA reset
> to finish. This is luxurious, :)
>
> According to the AHCI 1.2 spec, We should poll the HOST_CTL register,
> and return error if the host reset is not finished within 1 second.
>
> Test results show that the HBA reset can be done quickly(in usecs).
> And this patch may save nearly 1 second during resume.
That's a lot.
How heavily has it been tested?
Rafael
> Signed-off-by: Zhang Rui <rui.zhang@xxxxxxxxx>
> --
> drivers/ata/ahci.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> Index: linux-2.6/drivers/ata/ahci.c
> ===================================================================
> --- linux-2.6.orig/drivers/ata/ahci.c 2007-05-03 11:06:33.000000000 +0800
> +++ linux-2.6/drivers/ata/ahci.c 2008-07-02 16:25:54.000000000 +0800
> @@ -1073,18 +1073,29 @@
>
> /* global controller reset */
> if (!ahci_skip_host_reset) {
> + int delay = msecs_to_jiffies(1000);
> + int timeout;
> +
> tmp = readl(mmio + HOST_CTL);
> if ((tmp & HOST_RESET) == 0) {
> writel(tmp | HOST_RESET, mmio + HOST_CTL);
> readl(mmio + HOST_CTL); /* flush */
> }
>
> - /* reset must complete within 1 second, or
> + /*
> + * to perform host reset, OS should set HOST_RESET
> + * and poll until this bit is read to be "0"
> + * reset must complete within 1 second, or
> * the hardware should be considered fried.
> */
> - ssleep(1);
> + timeout = jiffies + delay;
> + while (jiffies < timeout) {
> + tmp = readl(mmio + HOST_CTL);
> + if (!(tmp & HOST_RESET))
> + break;
> + cpu_relax();
> + }
>
> - tmp = readl(mmio + HOST_CTL);
> if (tmp & HOST_RESET) {
> dev_printk(KERN_ERR, host->dev,
> "controller reset failed (0x%x)\n", tmp);
>
>
>
>
--
"Premature optimization is the root of all evil." - Donald Knuth
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