3.16.82-rc1 review patch. If anyone has any objections, please let me know.
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From: Miquel Raynal miquel.raynal@bootlin.com
commit 69c7f4618c16b4678f8a4949b6bb5ace259c0033 upstream.
Any write with either dd or flashcp to a device driven by the spear_smi.c driver will pass through the spear_smi_cpy_toio() function. This function will get called for chunks of up to 256 bytes. If the amount of data is smaller, we may have a problem if the data length is not 4-byte aligned. In this situation, the kernel panics during the memcpy:
# dd if=/dev/urandom bs=1001 count=1 of=/dev/mtd6 spear_smi_cpy_toio [620] dest c9070000, src c7be8800, len 256 spear_smi_cpy_toio [620] dest c9070100, src c7be8900, len 256 spear_smi_cpy_toio [620] dest c9070200, src c7be8a00, len 256 spear_smi_cpy_toio [620] dest c9070300, src c7be8b00, len 233 Unhandled fault: external abort on non-linefetch (0x808) at 0xc90703e8 [...] PC is at memcpy+0xcc/0x330
The above error occurs because the implementation of memcpy_toio() tries to optimize the number of I/O by writing 4 bytes at a time as much as possible, until there are less than 4 bytes left and then switches to word or byte writes.
Unfortunately, the specification states about the Write Burst mode:
"the next AHB Write request should point to the next incremented address and should have the same size (byte, half-word or word)"
This means ARM architecture implementation of memcpy_toio() cannot reliably be used blindly here. Workaround this situation by update the write path to stick to byte access when the burst length is not multiple of 4.
Fixes: f18dbbb1bfe0 ("mtd: ST SPEAr: Add SMI driver for serial NOR flash") Cc: Russell King linux@armlinux.org.uk Cc: Boris Brezillon boris.brezillon@collabora.com Signed-off-by: Miquel Raynal miquel.raynal@bootlin.com Reviewed-by: Russell King rmk+kernel@armlinux.org.uk Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/mtd/devices/spear_smi.c | 38 ++++++++++++++++++++++++++++++++- 1 file changed, 37 insertions(+), 1 deletion(-)
--- a/drivers/mtd/devices/spear_smi.c +++ b/drivers/mtd/devices/spear_smi.c @@ -595,6 +595,26 @@ static int spear_mtd_read(struct mtd_inf return 0; }
+/* + * The purpose of this function is to ensure a memcpy_toio() with byte writes + * only. Its structure is inspired from the ARM implementation of _memcpy_toio() + * which also does single byte writes but cannot be used here as this is just an + * implementation detail and not part of the API. Not mentioning the comment + * stating that _memcpy_toio() should be optimized. + */ +static void spear_smi_memcpy_toio_b(volatile void __iomem *dest, + const void *src, size_t len) +{ + const unsigned char *from = src; + + while (len) { + len--; + writeb(*from, dest); + from++; + dest++; + } +} + static inline int spear_smi_cpy_toio(struct spear_smi *dev, u32 bank, void __iomem *dest, const void *src, size_t len) { @@ -617,7 +637,23 @@ static inline int spear_smi_cpy_toio(str ctrlreg1 = readl(dev->io_base + SMI_CR1); writel((ctrlreg1 | WB_MODE) & ~SW_MODE, dev->io_base + SMI_CR1);
- memcpy_toio(dest, src, len); + /* + * In Write Burst mode (WB_MODE), the specs states that writes must be: + * - incremental + * - of the same size + * The ARM implementation of memcpy_toio() will optimize the number of + * I/O by using as much 4-byte writes as possible, surrounded by + * 2-byte/1-byte access if: + * - the destination is not 4-byte aligned + * - the length is not a multiple of 4-byte. + * Avoid this alternance of write access size by using our own 'byte + * access' helper if at least one of the two conditions above is true. + */ + if (IS_ALIGNED(len, sizeof(u32)) && + IS_ALIGNED((uintptr_t)dest, sizeof(u32))) + memcpy_toio(dest, src, len); + else + spear_smi_memcpy_toio_b(dest, src, len);
writel(ctrlreg1, dev->io_base + SMI_CR1);