[RFC] mmc: meson-gx: use memcpy_to/fromio for dram-access-quirk

[Neil Armstrong]

It has been reported that usage of memcpy() to/from an iomem mapping is invalid,
and and recent arm64 memcpy update [1] triggers a memory abort when dram-access-quirk
is used on the G12A/G12B platforms.

This adds a local sg_copy_to_buffer which makes usage of io versions of memcpy
when dram-access-quirk is enabled.

Fixes: acdc8e71d9bb ("mmc: meson-gx: add dram-access-quirk")
Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>

[1] 285133040e6c ("arm64: Import latest memcpy()/memmove() implementation")

Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
---
Hi Ulf, Marek, Mark,

I haven't tested the patch yet, but should fix issue reported at [2].

Neil

[2] https://lore.kernel.org/r/acb244ad-0759-5a96-c659-5c23003d3dcd@xxxxxxxxxxx

 drivers/mmc/host/meson-gx-mmc.c | 48 ++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
index b8b771b643cc..89ff6038092d 100644
--- a/drivers/mmc/host/meson-gx-mmc.c
+++ b/drivers/mmc/host/meson-gx-mmc.c
@@ -742,6 +742,48 @@ static void meson_mmc_desc_chain_transfer(struct mmc_host *mmc, u32 cmd_cfg)
 	writel(start, host->regs + SD_EMMC_START);
 }
 
+/* local sg copy to buffer version with _to/fromio usage for dram_access_quirk */
+static void meson_mmc_copy_buffer(struct meson_host *host, struct mmc_data *data,
+				  size_t buflen, bool to_buffer)
+{
+	unsigned int sg_flags = SG_MITER_ATOMIC;
+	struct scatterlist *sgl = data->sg;
+	unsigned int nents = data->sg_len;
+	struct sg_mapping_iter miter;
+	void *buf = host->bounce_buf;
+	unsigned int offset = 0;
+
+	if (to_buffer)
+		sg_flags |= SG_MITER_FROM_SG;
+	else
+		sg_flags |= SG_MITER_TO_SG;
+
+	sg_miter_start(&miter, sgl, nents, sg_flags);
+
+	while ((offset < buflen) && sg_miter_next(&miter)) {
+		unsigned int len;
+
+		len = min(miter.length, buflen - offset);
+
+		/* When dram_access_quirk, the bounce buffer is a iomem mapping */
+		if (host->dram_access_quirk) {
+			if (to_buffer)
+				memcpy_toio(buf + offset, miter.addr, len);
+			else
+				memcpy_fromio(miter.addr, buf + offset, len);
+		} else {
+			if (to_buffer)
+				memcpy(buf + offset, miter.addr, len);
+			else
+				memcpy(miter.addr, buf + offset, len);
+		}
+
+		offset += len;
+	}
+
+	sg_miter_stop(&miter);
+}
+
 static void meson_mmc_start_cmd(struct mmc_host *mmc, struct mmc_command *cmd)
 {
 	struct meson_host *host = mmc_priv(mmc);
@@ -785,8 +827,7 @@ static void meson_mmc_start_cmd(struct mmc_host *mmc, struct mmc_command *cmd)
 		if (data->flags & MMC_DATA_WRITE) {
 			cmd_cfg |= CMD_CFG_DATA_WR;
 			WARN_ON(xfer_bytes > host->bounce_buf_size);
-			sg_copy_to_buffer(data->sg, data->sg_len,
-					  host->bounce_buf, xfer_bytes);
+			meson_mmc_copy_buffer(host, data, xfer_bytes, true);
 			dma_wmb();
 		}
 
@@ -955,8 +996,7 @@ static irqreturn_t meson_mmc_irq_thread(int irq, void *dev_id)
 	if (meson_mmc_bounce_buf_read(data)) {
 		xfer_bytes = data->blksz * data->blocks;
 		WARN_ON(xfer_bytes > host->bounce_buf_size);
-		sg_copy_from_buffer(data->sg, data->sg_len,
-				    host->bounce_buf, xfer_bytes);
+		meson_mmc_copy_buffer(host, data, xfer_bytes, false);
 	}
 
 	next_cmd = meson_mmc_get_next_command(cmd);
-- 
2.25.1