linux-kernel - [PATCH 1/2] mmc: sdhci: add quirk to disable the bounce buffer

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Message-ID: <20251006013700.2272166-2-officialTechflashYT@gmail.com>
Date: Sun,  5 Oct 2025 18:36:59 -0700
From: Michael Garofalo <officialtechflashyt@...il.com>
To: adrian.hunter@...el.com,
	ulf.hansson@...aro.org
Cc: linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Michael Garofalo <officialTechflashYT@...il.com>
Subject: [PATCH 1/2] mmc: sdhci: add quirk to disable the bounce buffer

On some controllers, using a bounce buffer can have negative effects.
For example, on the SDHCI controller in the Nintendo Wii's "Hollywood"
chipset, using bounce buffers causes the internal Broadcom 4318 Wi-Fi to
fail on most data transfers.  The SDHCI core already supports running
without bounce buffers, so this exposes a quirk to forcibly disable them
for a given controller.

Signed-off-by: Michael Garofalo <officialTechflashYT@...il.com>
---
 drivers/mmc/host/sdhci.c | 8 +++++---
 drivers/mmc/host/sdhci.h | 4 ++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index ac7e11f37af7..7bf531802057 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -4806,9 +4806,11 @@ int sdhci_setup_host(struct sdhci_host *host)
 	 */
 	mmc->max_blk_count = (host->quirks & SDHCI_QUIRK_NO_MULTIBLOCK) ? 1 : 65535;
 
-	if (mmc->max_segs == 1)
-		/* This may alter mmc->*_blk_* parameters */
-		sdhci_allocate_bounce_buffer(host);
+	if (!(host->quirks2 & SDHCI_QUIRK2_NO_BOUNCE_BUFFER)) {
+		if (mmc->max_segs == 1)
+			/* This may alter mmc->*_blk_* parameters */
+			sdhci_allocate_bounce_buffer(host);
+	}
 
 	return 0;
 
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 58fcbeaf281e..9a082add96db 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -536,6 +536,10 @@ struct sdhci_host {
 #define SDHCI_QUIRK2_USE_32BIT_BLK_CNT			(1<<18)
 /* Issue CMD and DATA reset together */
 #define SDHCI_QUIRK2_ISSUE_CMD_DAT_RESET_TOGETHER	(1<<19)
+/*
+ * Bounce buffers cannot work, don't use them.
+ */
+#define SDHCI_QUIRK2_NO_BOUNCE_BUFFER			(1<<20)
 
 	int irq;		/* Device IRQ */
 	void __iomem *ioaddr;	/* Mapped address */
-- 
2.51.0