linux-kernel - [PATCH] mmc: meson-gx: limit segments to 1 when dram-access-quirk is needed

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Message-Id: <20200608084458.32014-1-narmstrong@baylibre.com>
Date:   Mon,  8 Jun 2020 10:44:58 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     ulf.hansson@...aro.org
Cc:     linux-amlogic@...ts.infradead.org, linux-mmc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Neil Armstrong <narmstrong@...libre.com>,
        Art Nikpal <art@...das.com>,
        Christian Hewitt <christianshewitt@...il.com>
Subject: [PATCH] mmc: meson-gx: limit segments to 1 when dram-access-quirk is needed

The actual max_segs computation leads to failure while using the broadcom
sdio brcmfmac/bcmsdh driver, since the driver tries to make usage of scatter
gather.

But with the dram-access-quirk we use a 1,5K SRAM bounce buffer, and the
max_segs current value of 3 leads to max transfers to 4,5k, which doesn't work.

This patch sets max_segs to 1 to better describe the hardware limitation,
and fix the SDIO functionnality with the brcmfmac/bcmsdh driver on Amlogic
G12A/G12B SoCs on boards like SEI510 or Khadas VIM3.

Reported-by: Art Nikpal <art@...das.com>
Reported-by: Christian Hewitt <christianshewitt@...il.com>
Fixes: acdc8e71d9bb ("mmc: meson-gx: add dram-access-quirk")
Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
---
 drivers/mmc/host/meson-gx-mmc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
index 35400cf2a2e4..cfaf8e7e22ec 100644
--- a/drivers/mmc/host/meson-gx-mmc.c
+++ b/drivers/mmc/host/meson-gx-mmc.c
@@ -1143,9 +1143,11 @@ static int meson_mmc_probe(struct platform_device *pdev)
 
 	mmc->caps |= MMC_CAP_CMD23;
 	if (host->dram_access_quirk) {
+		/* Limit segments to 1 due to low available sram memory */
+		mmc->max_segs = 1;
 		/* Limit to the available sram memory */
-		mmc->max_segs = SD_EMMC_SRAM_DATA_BUF_LEN / mmc->max_blk_size;
-		mmc->max_blk_count = mmc->max_segs;
+		mmc->max_blk_count = SD_EMMC_SRAM_DATA_BUF_LEN /
+				     mmc->max_blk_size;
 	} else {
 		mmc->max_blk_count = CMD_CFG_LENGTH_MASK;
 		mmc->max_segs = SD_EMMC_DESC_BUF_LEN /
-- 
2.22.0