[v1,2/3] ata: Fix the link down in first attempt for the APM X-Gene SoC AHCI SATA host controller driver.

This patch fixes the link down issue by retry for the APM X-Gene SoC
SATA host controller driver. Due to board design issue and short margin
limitation, it is observed that once out of many thousands power cycle
test, the sata link may not link up.

Signed-off-by: Loc Ho <lho@apm.com>
Signed-off-by: Suman Tripathi <stripathi@apm.com>
---
 drivers/ata/ahci_xgene.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

--
1.8.2.1

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Hello,

On Mon, Jun 23, 2014 at 03:45:37PM +0530, Suman Tripathi wrote:
> @@ -234,15 +237,20 @@ static int xgene_ahci_do_hardreset(struct ata_link *link,
>  	u8 *d2h_fis = pp->rx_fis + RX_FIS_D2H_REG;
>  	void __iomem *port_mmio = ahci_port_base(ap);
>  	struct ata_taskfile tf;
> +	int link_down_retry = 0;
>  	int rc;
>  	u32 val;
> 
> -	/* clear D2H reception area to properly wait for D2H FIS */
> -	ata_tf_init(link->device, &tf);
> -	tf.command = ATA_BUSY;
> -	ata_tf_to_fis(&tf, 0, 0, d2h_fis);
> -	rc = sata_link_hardreset(link, timing, deadline, online,
> +	do {
> +		/* clear D2H reception area to properly wait for D2H FIS */
> +		ata_tf_init(link->device, &tf);
> +		tf.command = ATA_BUSY;
> +		ata_tf_to_fis(&tf, 0, 0, d2h_fis);
> +		rc = sata_link_hardreset(link, timing, deadline, online,
>  				 ahci_check_ready);
> +		if (*online)
> +			break;
> +	} while (link_down_retry++ < MAX_LINK_DOWN_RETRY);

Hmm... so it's retrying w/o extending deadline if the link is reported
to be offline.  This definitely needs comment explaining what's going
on.  Wouldn't it make more sense to change @timing instead rather than
retrying resets?  sata_sil24 already does something similar.  Does,
f.e., using sata_deb_timing_long for @timing make the problem go away?

Thanks.