[PATCH] dmaengine: at_hdmac: fix sparse '__iomem' cast warning in memset helpers

[PATCH] dmaengine: at_hdmac: fix sparse '__iomem' cast warning in memset helpers

[Rosen Penev]

Both atc_prep_dma_memset() and atc_prep_dma_memset_sg() declare vaddr
as 'void __iomem *' but assign the return of dma_pool_alloc(), which
returns 'void *' (not iomem memory). This causes sparse to warn about
a cast removing the __iomem address space at the dereference site.

The struct field memset_vaddr is also typed as 'int *', which is
neither the type returned by dma_pool_alloc() nor the type used for
the actual writes.

Fix by declaring vaddr as 'u32 *' in both functions and changing
memset_vaddr in struct at_desc from 'int *' to 'u32 *'. This matches
the actual usage and eliminates the need for the (u32 *) cast.

Fixes: 5d8c5bea0da9 ("dmaengine: at_hdmac: add COMPILE_TEST support")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202607231110.8MqNRj0Q-lkp@intel.com/
Assisted-by: opencode:big-pickle
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/dma/at_hdmac.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index e5b30a57c477..f9c336630fa2 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -244,7 +244,7 @@ struct at_desc {
 	/* Memset temporary buffer */
 	bool				memset_buffer;
 	dma_addr_t			memset_paddr;
-	int				*memset_vaddr;
+	u32				*memset_vaddr;
 	struct atdma_sg			sg[] __counted_by(sglen);
 };
 
@@ -1097,7 +1097,7 @@ atc_prep_dma_memset(struct dma_chan *chan, dma_addr_t dest, int value,
 	struct at_dma_chan	*atchan = to_at_dma_chan(chan);
 	struct at_dma		*atdma = to_at_dma(chan->device);
 	struct at_desc		*desc;
-	void __iomem		*vaddr;
+	u32			*vaddr;
 	dma_addr_t		paddr;
 	char			fill_pattern;
 	int			ret;
@@ -1126,10 +1126,10 @@ atc_prep_dma_memset(struct dma_chan *chan, dma_addr_t dest, int value,
 	/* Only the first byte of value is to be used according to dmaengine */
 	fill_pattern = (char)value;
 
-	*(u32*)vaddr = (fill_pattern << 24) |
-		       (fill_pattern << 16) |
-		       (fill_pattern << 8) |
-		       fill_pattern;
+	*vaddr = (fill_pattern << 24) |
+		 (fill_pattern << 16) |
+		 (fill_pattern << 8) |
+		  fill_pattern;
 
 	desc = kzalloc_flex(*desc, sg, 1, GFP_ATOMIC);
 	if (!desc)
@@ -1168,7 +1168,7 @@ atc_prep_dma_memset_sg(struct dma_chan *chan,
 	struct at_dma		*atdma = to_at_dma(chan->device);
 	struct at_desc		*desc;
 	struct scatterlist	*sg;
-	void __iomem		*vaddr;
+	u32			*vaddr;
 	dma_addr_t		paddr;
 	size_t			total_len = 0;
 	int			i;
-- 
2.55.0

Re: [PATCH] dmaengine: at_hdmac: fix sparse '__iomem' cast warning in memset helpers

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

New issues:
- [Low] The patch leaves a redundant `(u32 *)` cast in `atc_prep_dma_memset_sg()` despite the commit message claiming to eliminate it.

Pre-existing issues:
- [High] Scatter-gather memset does not duplicate the fill byte across the 32-bit hardware transfer word, breaking memset for non-zero values.
--

--- Patch [1]: [PATCH] dmaengine: at_hdmac: fix sparse '__iomem' cast warning in memset helpers ---
commit dc753f3b1d4af7a33d407969b7dd8472cf0ea85c
Author: Rosen Penev <rosenp@gmail.com>

dmaengine: at_hdmac: fix sparse '__iomem' cast warning in memset helpers

This commit fixes a sparse warning caused by assigning a dma pool pointer
to an iomem pointer. It changes the type of the memset_vaddr to match its
actual usage and removes the need for type casting.

Link: https://lore.kernel.org/oe-kbuild-all/202607231110.8MqNRj0Q-lkp@intel.com/

> diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
> index e5b30a57c477a..f9c336630fa25 100644
> --- a/drivers/dma/at_hdmac.c
> +++ b/drivers/dma/at_hdmac.c

[ ... ]

> @@ -1168,7 +1168,7 @@ atc_prep_dma_memset_sg(struct dma_chan *chan,
>  	struct at_dma		*atdma = to_at_dma(chan->device);
>  	struct at_desc		*desc;
>  	struct scatterlist	*sg;
> -	void __iomem		*vaddr;
> +	u32			*vaddr;
>  	dma_addr_t		paddr;
>  	size_t			total_len = 0;
>  	int			i;

Further down in atc_prep_dma_memset_sg(), the code assigns the fill value
to vaddr:

> 	*(u32*)vaddr = value;

[Severity: High]
This is a pre-existing issue, but does this assignment properly duplicate the
fill byte across the 32-bit transfer word for non-zero values?

In atc_prep_dma_memset(), the fill pattern is explicitly shifted and combined
across all 4 bytes. Here it seems to just assign the raw value directly. Could
this result in the DMA hardware copying a pattern like 0x000000AB instead of
0xABABABAB, zeroing out 3 out of every 4 bytes for non-zero fills?

[Severity: Low]
This isn't a bug, but since vaddr is now declared as u32 *, is the (u32 *)
cast still needed here?

The commit message states that changing the vaddr type eliminates the need for
the cast, but it looks like the cast was only removed in atc_prep_dma_memset()
and remains here in atc_prep_dma_memset_sg().

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260723050335.270146-1-rosenp@gmail.com?part=1