linux-kernel - [PATCH v4] ata: increase retry count but shorten duration for Calxeda controller

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Message-Id: <1370265774-13939-1-git-send-email-mark.langsdorf@calxeda.com>
Date:	Mon,  3 Jun 2013 08:22:54 -0500
From:	Mark Langsdorf <mark.langsdorf@...xeda.com>
To:	tj@...nel.org, timur@...i.org, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, clemens@...isch.de,
	sergei.shtylyov@...entembedded.com
Cc:	Mark Langsdorf <mark.langsdorf@...xeda.com>
Subject: [PATCH v4] ata: increase retry count but shorten duration for Calxeda controller

Increase the retry count for the hard reset function to 100 but
shorten the time out period to 500 ms. See the comment for
ahci_highbank_hardreset for the reasons why those vaulues were
chosen.

Signed-off-by: Mark Langsdorf <mark.langsdorf@...xeda.com>
---
Changes from v3
	Move the detail to a comment on the ahci_highbank_hardreset function
Changes from v2
        Add static to the timing variable definition
Changes from v1
        Add const to the timing variable definition
        Added more detail in why the various numbers were chosen

 drivers/ata/sata_highbank.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/ata/sata_highbank.c b/drivers/ata/sata_highbank.c
index b20aa96..c846fd3 100644
--- a/drivers/ata/sata_highbank.c
+++ b/drivers/ata/sata_highbank.c
@@ -196,10 +196,26 @@ static int highbank_initialize_phys(struct device *dev, void __iomem *addr)
 	return 0;
 }
 
+/*
+ * The Calxeda SATA phy intermittently fails to bring up a link with Gen3
+ * Retrying the phy hard reset can work around the issue, but the drive
+ * may fail again. In less than 150 out of 15000 test runs, it took more
+ * than 10 tries for the link to be established (but never more than 35).
+ * Triple the maximum observed retry count to provide plenty of margin for
+ * rare events and to guarantee that the link is established.
+ *
+ * Also, the default 2 second time-out on a failed drive is too long in
+ * this situation. The uboot implementation of the same driver function
+ * uses a much shorter time-out period and never experiences a time out
+ * issue. Reducing the time-out to 500ms improves the responsiveness.
+ * The other timing constants were kept the same as the stock AHCI driver.
+ * This change was also tested 15000 times on 24 drives and none of them
+ * experienced a time out.
+ */
 static int ahci_highbank_hardreset(struct ata_link *link, unsigned int *class,
 				unsigned long deadline)
 {
-	const unsigned long *timing = sata_ehc_deb_timing(&link->eh_context);
+	static const unsigned long timing[] = { 5, 100, 500};
 	struct ata_port *ap = link->ap;
 	struct ahci_port_priv *pp = ap->private_data;
 	u8 *d2h_fis = pp->rx_fis + RX_FIS_D2H_REG;
@@ -207,7 +223,7 @@ static int ahci_highbank_hardreset(struct ata_link *link, unsigned int *class,
 	bool online;
 	u32 sstatus;
 	int rc;
-	int retry = 10;
+	int retry = 100;
 
 	ahci_stop_engine(ap);
 
-- 
1.8.1.2

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