Re: [PATCH] PCI: epf-mhi: return 0 on success instead of positive jiffies

[Manivannan Sadhasivam]

On Fri, Feb 27, 2026 at 01:15:10PM -0600, Bjorn Helgaas wrote:
> On Fri, Feb 06, 2026 at 03:05:29PM -0500, Daniel Hodges wrote:
> > wait_for_completion_timeout() returns the number of jiffies remaining
> > on success (positive value) or 0 on timeout. The pci_epf_mhi_edma_read()
> > and pci_epf_mhi_edma_write() functions use the return value directly as
> > their own return value, only converting timeout (0) to -ETIMEDOUT.
> > 
> > On success, they return the positive jiffies value. The callers in
> > drivers/bus/mhi/ep/ring.c check for errors with "if (ret < 0)" for
> > read_sync and "if (ret)" for write_sync. This causes write_sync success
> > cases to be incorrectly treated as errors since the positive jiffies
> > value is non-zero.
> > 
> > Fix by setting ret to 0 when wait_for_completion_timeout() succeeds.
> > 
> > Fixes: 7b99aaaddabb ("PCI: epf-mhi: Add eDMA support")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Daniel Hodges <git@xxxxxxxxxxxxxxxx>
> 
> Thanks for the patch!
> 
> Two questions: first, is there any reason why __mhi_ep_cache_ring()
> tests for "ret < 0" but mhi_ep_ring_add_element() tests for "ret"
> (non-zero)?  Could/should they both test just for non-zero, which I
> think is the typical style?
> 

Yes, agree. I've sent a patch to fix this. Thanks for spotting!

> Second, the subject and commit log are perfectly correct but basically
> at the level of describing the C code.  I propose something along
> these lines:
> 
>   PCI: epf-mhi: Return 0, not remaining timeout, when eDMA ops complete
> 
>   pci_epf_mhi_edma_read() and pci_epf_mhi_edma_write() start DMA
>   operations and wait for completion with a timeout.
> 
>   On successful completion, they previously returned the remaining
>   timeout, which callers may treat as an error.  In particular,
>   mhi_ep_ring_add_element(), which calls pci_epf_mhi_edma_write() via
>   mhi_cntrl->write_sync(), interprets any non-zero return value as
>   failure.
> 
>   Return 0 on success instead of the remaining timeout to prevent
>   mhi_ep_ring_add_element() from treating successful completion as an
>   error.
> 

Ammended the commit with the above, thanks!

- Mani

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