Re: [PATCH v1 00/16] .map_sg() error cleanup

On Thu, Jul 15, 2021 at 10:45:28AM -0600, Logan Gunthorpe wrote:

Hi,

This series is spun out and expanded from my work to add P2PDMA support
to DMA map operations[1].

The P2PDMA work requires distinguishing different error conditions in
a map_sg operation. dma_map_sgtable() already allows for returning an
error code (where as dma_map_sg() is only allowed to return zero)
however, it currently only returns -EINVAL when a .map_sg() call returns
zero.

This series cleans up all .map_sg() implementations to return appropriate
error codes. After the cleanup, dma_map_sg() will still return zero,
however dma_map_sgtable() will pass the error code from the .map_sg()
call. Thanks go to Martn Oliveira for doing a lot of the cleanup of the
obscure implementations.

The patch set is based off of v5.14-rc1 and a git repo can be found
here:

Have all the callers for dma_map_sg() been updated to check for error
codes? If not, isn't that a pre-requisit to this patch set?

From what I see in Linus' current tree, we still have cases today
where the return value of dma_map_sg() is compared with zero to
detect failure, so I think that needs fixing before we start changing
the dma_map_sg() implementation to return negative numbers.

I also notice that there are various places that don't check the
return value - and returning a negative number instead of zero may
well cause random other bits to be set in fields.

So, I think there's a fair amount of work to do in all the drivers
before this change can be considered.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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