[U-Boot] [PATCH v2] rockchip: mmc: rk3399: work around DMA issue in SPL

[Philipp Tomsich <philipp.tomsich@theobroma-systems.com>]

The RK3399 hangs during DMA of the Designware MMC controller, when
performing DMA-based transactions in SPL.  To work around this issue,
we disable DMA-based access modes in the SPL stage.

With this fix in place, we can now drop 'fifo-mode' in the DTS for the
RK3399-Q7 (Puma).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

---

Changes in v2:
- Fixes switching to fifo_mode (should have been 1) in SPL. I broke
  this at the 11th hour due to sloppy preparation of the patch.

 arch/arm/dts/rk3399-puma.dts  |  1 -
 drivers/mmc/rockchip_dw_mmc.c | 11 +++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm/dts/rk3399-puma.dts b/arch/arm/dts/rk3399-puma.dts
index 917df1e..71eb72d 100644
--- a/arch/arm/dts/rk3399-puma.dts
+++ b/arch/arm/dts/rk3399-puma.dts
@@ -91,7 +91,6 @@
 &sdmmc {
         u-boot,dm-pre-reloc;
 	bus-width = <4>;
-	fifo-mode; /* until we fix DMA in SPL */
 	status = "okay";
 };
 
diff --git a/drivers/mmc/rockchip_dw_mmc.c b/drivers/mmc/rockchip_dw_mmc.c
index c36eda0..5b4ed7a 100644
--- a/drivers/mmc/rockchip_dw_mmc.c
+++ b/drivers/mmc/rockchip_dw_mmc.c
@@ -76,6 +76,17 @@ static int rockchip_dwmmc_ofdata_to_platdata(struct udevice *dev)
 		return -EINVAL;
 	priv->fifo_mode = fdtdec_get_bool(gd->fdt_blob, dev_of_offset(dev),
 					  "fifo-mode");
+
+#if defined(CONFIG_ROCKCHIP_RK3399) && defined(CONFIG_SPL_BUILD)
+	/*
+	 * For a RK3399 SPL build, force fifo_mode to on (i.e. disable
+	 * DMA) as the MMC transaction will otherwise hang. This issue
+	 * reproduces only for SPL (i.e. BL2 in the ATF terminology),
+	 * but doesn't occur with the full U-Boot stage.
+	 */
+	priv->fifo_mode = 1;
+#endif
+
 	if (fdtdec_get_int_array(gd->fdt_blob, dev_of_offset(dev),
 				 "clock-freq-min-max", priv->minmax, 2))
 		return -EINVAL;
-- 
1.9.1