Re: [PATCH v4] iommu/amd: Enhance "Completion-wait Time-out" error message

[Ankit Soni]

On Tue, Nov 11, 2025 at 04:54:40PM +0530, Dheeraj Kumar Srivastava wrote:
> Hi Ankit,
> 
> Thanks for reviewing the patch.
> 
> On 11/7/2025 7:36 PM, Ankit Soni wrote:
> > Hello Dheeraj,
> > 
> > On Wed, Nov 05, 2025 at 01:33:42PM +0530, Dheeraj Kumar Srivastava wrote:
> > > Current IOMMU driver prints "Completion-wait Time-out" error message with
> > > insufficient information to further debug the issue.
> > > 
> > > Enhancing the error message as following:
> > > 1. Log IOMMU PCI device ID in the error message.
> > > 2. With "amd_iommu_dump=1" kernel command line option, dump entire
> > >     command buffer entries including Head and Tail offset.
> > > 
> > > Dump the entire command buffer only on the first 'Completion-wait Time-out'
> > > to avoid dmesg spam.
> > > 
> > > Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@xxxxxxx>
> > > ---
> > > Changes since v3:
> > > -> Dump the entire command buffer only on the first 'Completion-wait Time-out'
> > >     when amd_iommu_dump=1, instead of dumping it on every occurrence.
> > > 
> > >   drivers/iommu/amd/amd_iommu_types.h |  4 ++++
> > >   drivers/iommu/amd/iommu.c           | 28 +++++++++++++++++++++++++++-
> > >   2 files changed, 31 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> > > index 95f63c5f6159..7576814f944d 100644
> > > --- a/drivers/iommu/amd/amd_iommu_types.h
> > > +++ b/drivers/iommu/amd/amd_iommu_types.h
> > > @@ -247,6 +247,10 @@
> > >   #define CMD_BUFFER_ENTRIES 512
> > >   #define MMIO_CMD_SIZE_SHIFT 56
> > >   #define MMIO_CMD_SIZE_512 (0x9ULL << MMIO_CMD_SIZE_SHIFT)
> > 
> > It's worth adding comment for MASK 4-18.
> > 
> 
> Sure.
> 
> > > +#define MMIO_CMD_HEAD_MASK	GENMASK_ULL(18, 4)
> > > +#define MMIO_CMD_BUFFER_HEAD(x) FIELD_GET(MMIO_CMD_HEAD_MASK, (x))
> > > +#define MMIO_CMD_TAIL_MASK	GENMASK_ULL(18, 4)
> > 
> > Since HEAD and TAIL masks are same, may be, you can use something like
> > MMIO_CMD_HEAD_TAIL_MASK().
> > 
> 
> Agree, but I’d prefer to keep them as separate definitions for clarity and
> potential future changes. Let me know if you have any further comments.
> 

Okay, that's fine.

> > > +#define MMIO_CMD_BUFFER_TAIL(x) FIELD_GET(MMIO_CMD_TAIL_MASK, (x))
> > >   /* constants for event buffer handling */
> > >   #define EVT_BUFFER_SIZE		8192 /* 512 entries */
> > > diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> > > index eb348c63a8d0..abce078d2323 100644
> > > --- a/drivers/iommu/amd/iommu.c
> > > +++ b/drivers/iommu/amd/iommu.c
> > > @@ -1156,6 +1156,25 @@ irqreturn_t amd_iommu_int_handler(int irq, void *data)
> > >    *
> > >    ****************************************************************************/
> > > +static void dump_command_buffer(struct amd_iommu *iommu)
> > > +{
> > > +	struct iommu_cmd *cmd;
> > > +	int head, tail, i;
> > 
> > Since readl returns u32, prefer u32 for head/tail to avoid any surprises
> > or sign-ext issues.
> 
> Sure.
> 
> > and similarly use %u in pr_err() below.
> 
> I’d prefer dumping the head and tail values as integers, so they can be
> easily mapped to the command buffer entries indexed by integer offsets. Let
> me know if you have any further comments?
> 

%u and %d will print same value for mask above. Since you were seeking
non negative value, it will be good to keep %u.

Otherwise patch looks good to me.

Reviewed-by: Ankit Soni <Ankit.Soni@xxxxxxx>

- Ankit
> > 
> > > +
> > > +	head = readl(iommu->mmio_base + MMIO_CMD_HEAD_OFFSET);
> > > +	tail = readl(iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
> > > +
> > > +	pr_err("CMD Buffer head=%d tail=%d\n", (int)(MMIO_CMD_BUFFER_HEAD(head)),
> > > +	       (int)(MMIO_CMD_BUFFER_TAIL(tail)));
> > > +
> > > +	for (i = 0; i < CMD_BUFFER_ENTRIES; i++) {
> > > +		cmd = (struct iommu_cmd *)(iommu->cmd_buf + i * sizeof(*cmd));
> > > +		pr_err("%3d: %08x %08x %08x %08x\n", i, cmd->data[0], cmd->data[1], cmd->data[2],
> > > +		       cmd->data[3]);
> > > +	}
> > > +}
> > > +
> > > +
> > 
> > Remove extra line.
> > 
> 
> Sure.
> 
> Thanks
> Dheeraj
> 
> > Best,
> > Ankit
> > 
> > >   static int wait_on_sem(struct amd_iommu *iommu, u64 data)
> > >   {
> > >   	int i = 0;
> > > @@ -1166,7 +1185,14 @@ static int wait_on_sem(struct amd_iommu *iommu, u64 data)
> > >   	}
> > >   	if (i == LOOP_TIMEOUT) {
> > > -		pr_alert("Completion-Wait loop timed out\n");
> > > +
> > > +		pr_alert("IOMMU %04x:%02x:%02x.%01x: Completion-Wait loop timed out\n",
> > > +			 iommu->pci_seg->id, PCI_BUS_NUM(iommu->devid),
> > > +			 PCI_SLOT(iommu->devid), PCI_FUNC(iommu->devid));
> > > +
> > > +		if (amd_iommu_dump)
> > > +			DO_ONCE_LITE(dump_command_buffer, iommu);
> > > +
> > >   		return -EIO;
> > >   	}
> > > -- 
> > > 2.25.1
> > > 
>