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* [PATCH v2] nvme: retain split access workaround for capability reads
@ 2019-10-03 11:57 Ard Biesheuvel
  2019-10-06  9:14 ` Christoph Hellwig
  0 siblings, 1 reply; 2+ messages in thread
From: Ard Biesheuvel @ 2019-10-03 11:57 UTC (permalink / raw)
  To: linux-nvme; +Cc: sagi, Ard Biesheuvel, ilias.apalodimas, axboe, kbusch, hch

Commit 7fd8930f26be4

  "nvme: add a common helper to read Identify Controller data"

has re-introduced an issue that we have attempted to work around in the
past, in commit a310acd7a7ea ("NVMe: use split lo_hi_{read,write}q").

The problem is that some PCIe NVMe controllers do not implement 64-bit
outbound accesses correctly, which is why the commit above switched
to using lo_hi_[read|write]q for all 64-bit BAR accesses occuring in
the code.

In the mean time, the NVMe subsystem has been refactored, and now calls
into the PCIe support layer for NVMe via a .reg_read64() method, which
fails to use lo_hi_readq(), and thus reintroduces the problem that the
workaround above aimed to address.

Given that, at the moment, .reg_read64() is only used to read the
capability register [which is known to tolerate split reads], let's
switch .reg_read64() to lo_hi_readq() as well.

This fixes a boot issue on some ARM boxes with NVMe behind a Synopsys
DesignWare PCIe host controller.

Fixes: 7fd8930f26be4 ("nvme: add a common helper to read Identify Controller data")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
v2: drop WARN_ON(), add reference to commit that [re-]introduced the issue

 drivers/nvme/host/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index c0808f9eb8ab..ee7ce7696a88 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2672,7 +2672,7 @@ 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);
+	*val = lo_hi_readq(to_nvme_dev(ctrl)->bar + off);
 	return 0;
 }
 
-- 
2.20.1


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^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH v2] nvme: retain split access workaround for capability reads
  2019-10-03 11:57 [PATCH v2] nvme: retain split access workaround for capability reads Ard Biesheuvel
@ 2019-10-06  9:14 ` Christoph Hellwig
  0 siblings, 0 replies; 2+ messages in thread
From: Christoph Hellwig @ 2019-10-06  9:14 UTC (permalink / raw)
  To: Ard Biesheuvel; +Cc: sagi, ilias.apalodimas, linux-nvme, axboe, kbusch, hch

>  static int nvme_pci_reg_read64(struct nvme_ctrl *ctrl, u32 off, u64 *val)
>  {
> -	*val = readq(to_nvme_dev(ctrl)->bar + off);
> +	*val = lo_hi_readq(to_nvme_dev(ctrl)->bar + off);

Please add a comment why we are doing this.

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Linux-nvme mailing list
Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2019-10-03 11:57 [PATCH v2] nvme: retain split access workaround for capability reads Ard Biesheuvel
2019-10-06  9:14 ` Christoph Hellwig

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