[PATCH v2] dmaengine: stm32-dma: avoid bitfield overflow assertion

[Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>]

stm32_dma_get_burst() returns a negative error for invalid input, which
gets turned into a large u32 value in stm32_dma_prep_dma_memcpy() that
in turn triggers an assertion because it does not fit into a two-bit field:
drivers/dma/stm32-dma.c: In function 'stm32_dma_prep_dma_memcpy':
include/linux/compiler_types.h:354:38: error: call to '__compiletime_assert_282' declared with attribute error: FIELD_PREP: value too large for the field
     _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
                                         ^
   include/linux/compiler_types.h:335:4: note: in definition of macro '__compiletime_assert'
       prefix ## suffix();    \
       ^~~~~~
   include/linux/compiler_types.h:354:2: note: in expansion of macro '_compiletime_assert'
     _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
     ^~~~~~~~~~~~~~~~~~~
   include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
    #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                        ^~~~~~~~~~~~~~~~~~
   include/linux/bitfield.h:68:3: note: in expansion of macro 'BUILD_BUG_ON_MSG'
      BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?  \
      ^~~~~~~~~~~~~~~~
   include/linux/bitfield.h:114:3: note: in expansion of macro '__BF_FIELD_CHECK'
      __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
      ^~~~~~~~~~~~~~~~
   drivers/dma/stm32-dma.c:1237:4: note: in expansion of macro 'FIELD_PREP'
       FIELD_PREP(STM32_DMA_SCR_PBURST_MASK, dma_burst) |
       ^~~~~~~~~~

As an easy workaround, assume the error can happen, so try to handle this
by failing stm32_dma_prep_dma_memcpy() before the assertion. It replicates
what is done in stm32_dma_set_xfer_param() where stm32_dma_get_burst() is
also used.

Fixes: 1c32d6c37cc2 ("dmaengine: stm32-dma: use bitfield helpers")
Fixes: a2b6103b7a8a ("dmaengine: stm32-dma: Improve memory burst management")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202311060135.Q9eMnpCL-lkp@xxxxxxxxx/
---
Updated from v1: https://lore.kernel.org/lkml/20230214103222.1193307-1-arnd@xxxxxxxxxx/T/
- change dma_burst from u32 to int, and check for negative value, as done
in stm32_dma_set_xfer_param()
- Add 'Cc:', 'Reported-by:' and 'Closes:' tags
---
 drivers/dma/stm32-dma.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 0b30151fb45c..9840594a6aaa 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -1249,8 +1249,8 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_dma_memcpy(
 	enum dma_slave_buswidth max_width;
 	struct stm32_dma_desc *desc;
 	size_t xfer_count, offset;
-	u32 num_sgs, best_burst, dma_burst, threshold;
-	int i;
+	u32 num_sgs, best_burst, threshold;
+	int dma_burst, i;
 
 	num_sgs = DIV_ROUND_UP(len, STM32_DMA_ALIGNED_MAX_DATA_ITEMS);
 	desc = kzalloc(struct_size(desc, sg_req, num_sgs), GFP_NOWAIT);
@@ -1268,6 +1268,10 @@ static struct dma_async_tx_descriptor *stm32_dma_prep_dma_memcpy(
 		best_burst = stm32_dma_get_best_burst(len, STM32_DMA_MAX_BURST,
 						      threshold, max_width);
 		dma_burst = stm32_dma_get_burst(chan, best_burst);
+		if (dma_burst < 0) {
+			kfree(desc);
+			return NULL;
+		}
 
 		stm32_dma_clear_reg(&desc->sg_req[i].chan_reg);
 		desc->sg_req[i].chan_reg.dma_scr =
-- 
2.25.1