[PATCH] mmc: sdhci: Fix max_seg_size for 64KiB PAGE_SIZE

[Adrian Hunter <adrian.hunter@intel.com>]

blk_queue_max_segment_size() ensured:

	if (max_size < PAGE_SIZE)
		max_size = PAGE_SIZE;

whereas:

blk_validate_limits() makes it an error:

	if (WARN_ON_ONCE(lim->max_segment_size < PAGE_SIZE))
		return -EINVAL;

The change from one to the other, exposed sdhci which was setting maximum
segment size too low in some circumstances.

Fix the maximum segment size when it is too low.

Fixes: 616f87661792 ("mmc: pass queue_limits to blk_mq_alloc_disk")
Cc: stable@vger.kernel.org
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 drivers/mmc/host/sdhci.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index a20df9383b20..4b91c9e96635 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -4708,6 +4708,21 @@ int sdhci_setup_host(struct sdhci_host *host)
 		if (host->quirks & SDHCI_QUIRK_BROKEN_ADMA_ZEROLEN_DESC) {
 			host->max_adma = 65532; /* 32-bit alignment */
 			mmc->max_seg_size = 65535;
+			/*
+			 * sdhci_adma_table_pre() expects to define 1 DMA
+			 * descriptor per segment, so the maximum segment size
+			 * is set accordingly. SDHCI allows up to 64KiB per DMA
+			 * descriptor (16-bit field), but some controllers do
+			 * not support "zero means 65536" reducing the maximum
+			 * for them to 65535. That is a problem if PAGE_SIZE is
+			 * 64KiB because the block layer does not support
+			 * max_seg_size < PAGE_SIZE, however
+			 * sdhci_adma_table_pre() has a workaround to handle
+			 * that case, and split the descriptor. Refer also
+			 * comment in sdhci_adma_table_pre().
+			 */
+			if (mmc->max_seg_size < PAGE_SIZE)
+				mmc->max_seg_size = PAGE_SIZE;
 		} else {
 			mmc->max_seg_size = 65536;
 		}
-- 
2.34.1