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Just like the I/O size we * require drivers to at least handle a full page per segment. */ ... if (WARN_ON_ONCE(lim->max_segment_size < PAGE_SIZE)) return -EINVAL; In case when IDMAC (Internal DMA Controller) is used, dw_mmc.c always sets .max_seg_size to 4 KiB: mmc->max_seg_size = 0x1000; The comment in the code above explains why it's incorrect. Arnd suggested setting .max_seg_size to .max_req_size to fix it, which is also what some other drivers are doing: $ grep -rl 'max_seg_size.*=.*max_req_size' drivers/mmc/host/ | \ wc -l 18 This change is not only fixing the boot with 16K/64K pages, but also leads to a better MMC performance. The linear write performance was tested on E850-96 board (eMMC only), before commit [1] (where it's possible to boot with 16K/64K pages without this fix, to be able to do a comparison). It was tested with this command: # dd if=/dev/zero of=somefile bs=1M count=500 oflag=sync Test results are as follows: - 4K pages, .max_seg_size = 4 KiB: 94.2 MB/s - 4K pages, .max_seg_size = .max_req_size = 512 KiB: 96.9 MB/s - 16K pages, .max_seg_size = 4 KiB: 126 MB/s - 16K pages, .max_seg_size = .max_req_size = 2 MiB: 128 MB/s - 64K pages, .max_seg_size = 4 KiB: 138 MB/s - 64K pages, .max_seg_size = .max_req_size = 8 MiB: 138 MB/s Unfortunately, SD card controller is not enabled in E850-96 yet, so it wasn't possible for me to run the test on some cheap SD cards to check this patch's impact on those. But it's possible that this change might also reduce the writes count, thus improving SD/eMMC longevity. All credit for the analysis and the suggested solution goes to Arnd. [1] https://lore.kernel.org/all/20240215070300.2200308-18-hch@lst.de/ Fixes: f95f3850f7a9 ("mmc: dw_mmc: Add Synopsys DesignWare mmc host driver.") Suggested-by: Arnd Bergmann Reported-by: Linux Kernel Functional Testing Closes: https://lore.kernel.org/all/CA+G9fYtddf2Fd3be+YShHP6CmSDNcn0ptW8qg+stUKW+Cn0rjQ@mail.gmail.com/ Signed-off-by: Sam Protsenko --- drivers/mmc/host/dw_mmc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c index 8e2d676b9239..cccd5633ff40 100644 --- a/drivers/mmc/host/dw_mmc.c +++ b/drivers/mmc/host/dw_mmc.c @@ -2951,8 +2951,8 @@ static int dw_mci_init_slot(struct dw_mci *host) if (host->use_dma == TRANS_MODE_IDMAC) { mmc->max_segs = host->ring_size; mmc->max_blk_size = 65535; - mmc->max_seg_size = 0x1000; - mmc->max_req_size = mmc->max_seg_size * host->ring_size; + mmc->max_req_size = DW_MCI_DESC_DATA_LENGTH * host->ring_size; + mmc->max_seg_size = mmc->max_req_size; mmc->max_blk_count = mmc->max_req_size / 512; } else if (host->use_dma == TRANS_MODE_EDMAC) { mmc->max_segs = 64;