From 2498363310e9b5e5de0e104709adc35c9f3ff7d9 Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Wed, 3 Nov 2021 16:33:12 +0100
Subject: [PATCH] dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width
Git-commit: 2498363310e9b5e5de0e104709adc35c9f3ff7d9
Patch-mainline: v5.16-rc1
References: git-fixes stable-5.14.19

[ backport note: only the first chunk was applied for SLE15-SP4 branch -- tiwai ]

Using the % operator on a 64-bit variable is expensive and can
cause a link failure:

Arm-linux-gnueabi-ld: drivers/dma/stm32-dma.o: in function `stm32_dma_get_max_width':
stm32-dma.c:(.text+0x170): undefined reference to `__aeabi_uldivmod'
Arm-linux-gnueabi-ld: drivers/dma/stm32-dma.o: in function `stm32_dma_set_xfer_param':
stm32-dma.c:(.text+0x1cd4): undefined reference to `__aeabi_uldivmod'

As we know that we just want to check the alignment in
stm32_dma_get_max_width(), there is no need for a full division, and
using a simple mask is a faster replacement.

Same in stm32_dma_set_xfer_param(), change this to only allow burst
transfers if the address is a multiple of the length.
stm32_dma_get_best_burst just after will take buf_len into account to fix
burst in case of misalignment.

Fixes: b20fd5fa310c ("dmaengine: stm32-dma: fix stm32_dma_get_max_width")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20211103153312.41483-1-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/dma/stm32-dma.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -278,7 +278,7 @@ static enum dma_slave_buswidth stm32_dma
 	       max_width > DMA_SLAVE_BUSWIDTH_1_BYTE)
 		max_width = max_width >> 1;
 
-	if (buf_addr % max_width)
+	if (buf_addr & (max_width - 1))
 		max_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
 
 	return max_width;