linux-kernel - [PATCH v2] sata_sil24: Use memory barriers before issuing commands

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Message-ID: <20100610160212.18091.29856.stgit@e102109-lin.cambridge.arm.com>
Date:	Thu, 10 Jun 2010 17:02:12 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Tejun Heo <tj@...nel.org>, Colin Tuckley <colin.tuckley@....com>,
	Jeff Garzik <jeff@...zik.org>
Subject: [PATCH v2] sata_sil24: Use memory barriers before issuing commands

The data in the cmd_block buffers may reach the main memory after the
writel() to the device ports. This patch introduces two calls to wmb()
to ensure the relative ordering.

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Tested-by: Colin Tuckley <colin.tuckley@....com>
Cc: Tejun Heo <tj@...nel.org>
Cc: Jeff Garzik <jeff@...zik.org>
---
 drivers/ata/sata_sil24.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index e925051..a5d5aff 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -622,6 +622,11 @@ static int sil24_exec_polled_cmd(struct ata_port *ap, int pmp,
 	irq_enabled = readl(port + PORT_IRQ_ENABLE_SET);
 	writel(PORT_IRQ_COMPLETE | PORT_IRQ_ERROR, port + PORT_IRQ_ENABLE_CLR);
 
+	/*
+	 * The barrier is required to ensure that writes to cmd_block reach
+	 * the memory before the write to PORT_CMD_ACTIVATE.
+	 */
+	wmb();
 	writel((u32)paddr, port + PORT_CMD_ACTIVATE);
 	writel((u64)paddr >> 32, port + PORT_CMD_ACTIVATE + 4);
 
@@ -895,6 +900,11 @@ static unsigned int sil24_qc_issue(struct ata_queued_cmd *qc)
 	paddr = pp->cmd_block_dma + tag * sizeof(*pp->cmd_block);
 	activate = port + PORT_CMD_ACTIVATE + tag * 8;
 
+	/*
+	 * The barrier is required to ensure that writes to cmd_block reach
+	 * the memory before the write to PORT_CMD_ACTIVATE.
+	 */
+	wmb();
 	writel((u32)paddr, activate);
 	writel((u64)paddr >> 32, activate + 4);
 

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