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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: linux-nvme@lists.infradead.org
Cc: sagi@grimberg.me, Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	ilias.apalodimas@linaro.org, axboe@fb.com, kbusch@kernel.org,
	hch@lst.de
Subject: [PATCH v4] nvme/pci: Split 8-byte reads
Date: Mon,  7 Oct 2019 20:22:44 +0200	[thread overview]
Message-ID: <20191007182244.8516-1-ard.biesheuvel@linaro.org> (raw)

The nvme pci driver had split 8-byte register reads using lo_hi_readq()
due to nvme controllers that do not support that sized access. This
behavior was inadvertently changed to readq(), which may break those
controllers. Restore the previous behavior.

Fixes: 7fd8930f26be4 ("nvme: add a common helper to read Identify Controller data")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
v4: update comment and commit text according to Keith's guidance
v3: add comment explaining why we need the split read
v2: drop WARN_ON(), add reference to commit that [re-]introduced the issue
---
 drivers/nvme/host/pci.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index bb88681f4dc3..3fe0c5185646 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2672,7 +2672,12 @@ static int nvme_pci_reg_write32(struct nvme_ctrl *ctrl, u32 off, u32 val)
 
 static int nvme_pci_reg_read64(struct nvme_ctrl *ctrl, u32 off, u64 *val)
 {
-	*val = readq(to_nvme_dev(ctrl)->bar + off);
+	/*
+	 * Split the 8-byte read into two 4-byte reads since all controllers
+	 * support 4 byte register reads, but some do not support the larger
+	 * access size.
+	 */
+	 *val = lo_hi_readq(to_nvme_dev(ctrl)->bar + off);
 	return 0;
 }
 
-- 
2.20.1


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             reply	other threads:[~2019-10-07 18:23 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 18:22 Ard Biesheuvel [this message]
2019-10-07 18:28 ` [PATCH v4] nvme/pci: Split 8-byte reads Keith Busch
2019-10-07 18:47 ` Christoph Hellwig

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