On Sat, Aug 07, 2021 at 03:11:34PM +0800, Dongdong Liu wrote:

On 2021/8/6 2:12, Bjorn Helgaas wrote:

quoted

On Wed, Aug 04, 2021 at 09:47:08PM +0800, Dongdong Liu wrote:

quoted

Add a 10-Bit Tag check in the P2PDMA code to ensure that a device with
10-Bit Tag Requester doesn't interact with a device that does not
support 10-BIT Tag Completer. Before that happens, the kernel should
emit a warning. "echo 0 > /sys/bus/pci/devices/.../10bit_tag" to
disable 10-BIT Tag Requester for PF device.
"echo 0 > /sys/bus/pci/devices/.../sriov_vf_10bit_tag_ctl" to disable
10-BIT Tag Requester for VF device.

s/10-BIT/10-Bit/ several times.

Will fix.

quoted

Add blank lines between paragraphs.

Will fix.

quoted

quoted

Signed-off-by: Dongdong Liu <redacted>
---
 drivers/pci/p2pdma.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 50cdde3..948f2be 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c

@@ -19,6 +19,7 @@
 #include <linux/random.h>
 #include <linux/seq_buf.h>
 #include <linux/xarray.h>
+#include "pci.h"

 enum pci_p2pdma_map_type {
 	PCI_P2PDMA_MAP_UNKNOWN = 0,

@@ -410,6 +411,41 @@ static unsigned long map_types_idx(struct pci_dev *client)
 		(client->bus->number << 8) | client->devfn;
 }

+static bool check_10bit_tags_vaild(struct pci_dev *a, struct pci_dev *b,

s/vaild/valid/

Or maybe s/valid/safe/ or s/valid/supported/, since "valid" isn't
quite the right word here.  We want to know whether the source is
enabled to generate 10-bit tags, and if so, whether the destination
can handle them.

"if (check_10bit_tags_valid())" does not make sense because
"check_10bit_tags_valid()" is not a question with a yes/no answer.

"10bit_tags_valid()" *might* be, because "if (10bit_tags_valid())"
makes sense.  But I don't think you can start with a digit.

Or maybe you want to invert the sense, e.g.,
"10bit_tags_unsupported()", since that avoids negation at the caller:

  if (10bit_tags_unsupported(a, b) ||
      10bit_tags_unsupported(b, a))
        map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;

Good suggestion. add a pci_ prefix.

if (pci_10bit_tags_unsupported(a, b) ||
    pci_10bit_tags_unsupported(b, a))
	map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED;

This treats both directions as equally important.  I don't know P2PDMA
very well, but that doesn't seem like it would necessarily be the
case.  I would think a common case would be device A doing DMA to B,
but B *not* doing DMA to A.  So can you tell which direction you're
setting up here, and can you take advantage of any asymmetry, e.g., by
enabling 10-bit tags in the direction that supports it even if the
other direction does not?