From cfc5ebc9540e29f8f96db88bbfa261139e5afedb Mon Sep 17 00:00:00 2001 From: Orgad Shaneh Date: Wed, 16 Sep 2026 16:27:31 +0000 Subject: [PATCH] mtd: cfi_cmdset_0002: cap the write-buffer chunk at 256 bytes on an x8 device The Write to Buffer command takes the number of words to program minus one, and do_write_buffer() sends that count as a single bus word: map_write(map, CMD(words - 1), cmd_adr); CMD() replicates the value into every device lane, so each device reads the count off its own data lines - eight of them on an x8 part. A count that does not fit in eight bits is truncated there, which limits one Write to Buffer to 256 words on an x8 device, however large a buffer the chip advertises in its CFI query. The M29EW on a Cavium Octeon CN6335 board (an x16 part strapped to x8) advertises MaxBufWriteSize = 512 bytes, so cfi_amdstd_write_buffers() split the data into 512-byte chunks and do_write_buffer() sent a count of 511. The chip saw 511 & 0xff = 255, expected 256 bytes, and aborted the program when the 257th arrived. Chunks below 256 bytes - the leading partial chunk of a write - completed normally, so only the full-size ones failed: MTD do_write_buffer_wait(): software timeout, address:0x03278bff. jffs2: Write of 4164 bytes at 0x02c789b4 failed. returned -5, retlen 68 jffs2: No space for garbage collection. Aborting GC thread Clamp MaxBufWriteSize for x8 devices in the write-buffer fixup, and recompute mtd->writebufsize, which cfi_cmdset_0002_setup() derives from MaxBufWriteSize before the fixups run. The clamp deliberately keys off the device width rather than the part, even though the driver already recognises this one in is_m29ew(): the ceiling comes from the width of a device's data bus, not from the chip, so any x8 device advertising a larger buffer is told a count it cannot receive. The M29EW is only where it was found. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: Orgad Shaneh Signed-off-by: Miquel Raynal --- drivers/mtd/chips/cfi_cmdset_0002.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c index 517db2f2707f..100cab95a17b 100644 --- a/drivers/mtd/chips/cfi_cmdset_0002.c +++ b/drivers/mtd/chips/cfi_cmdset_0002.c @@ -283,6 +283,21 @@ static void fixup_use_write_buffers(struct mtd_info *mtd) pr_debug("Using buffer write method\n"); mtd->_write = cfi_amdstd_write_buffers; } + + /* + * The word count of the Write to Buffer command is a single bus + * word per device, so an x8 device can be told to program at most + * 256 bytes however large a buffer it advertises - including when + * several of them are interleaved on a wider bus, where CMD() + * replicates the count into each device's lane and it is truncated + * there. + */ + if (cfi->device_type == CFI_DEVICETYPE_X8 && + cfi->cfiq->MaxBufWriteSize > 8) { + cfi->cfiq->MaxBufWriteSize = 8; + mtd->writebufsize = cfi_interleave(cfi) << + cfi->cfiq->MaxBufWriteSize; + } } #endif /* !FORCE_WORD_WRITE */