linux-kernel - [PATCH 4/4] dma: mxs-dma: Don't use CLKGATE bits in CTRL0 to disable DMA channels

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Message-Id: <689f40c73aabe244d65c52ce1ebb9e15220bc3c7.1323176362.git.LW@KARO-electronics.de>
Date:	Thu,  8 Dec 2011 09:15:44 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Huang Shijie <b32955@...escale.com>,
	Wolfram Sang <w.sang@...gutronix.de>,
	linux-kernel@...r.kernel.org,
	Lothar Waßmann <LW@...O-electronics.de>
Subject: [PATCH 4/4] dma: mxs-dma: Don't use CLKGATE bits in CTRL0 to disable DMA channels

This is how the original Freescale code (unintentionally) worked,
because the code path which would have asserted the CLKGATE bit was
never actually reached in their code.
This fixes the nefarious "DMA timout" bug when multiple DMA channels
(e.g. GPMI NAND and MMC) are used at the same time.
If a better fix for this problem should be found, the clkgate handling
could be reinstated.
See http://lists.infradead.org/pipermail/linux-arm-kernel/2011-September/065228.html

Also reverse the order of mxs_dma_disable_chan() and
mxs_dma_reset_chan() in mxs_dma_control() because mxs_dma_reset_chan()
can only work when the DMA channel is enabled.

Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
---
 drivers/dma/mxs-dma.c |   29 +----------------------------
 1 files changed, 1 insertions(+), 28 deletions(-)

diff --git a/drivers/dma/mxs-dma.c b/drivers/dma/mxs-dma.c
index 78336b0..71ba93a 100644
--- a/drivers/dma/mxs-dma.c
+++ b/drivers/dma/mxs-dma.c
@@ -44,7 +44,6 @@
 #define HW_APBHX_CTRL0				0x000
 #define BM_APBH_CTRL0_APB_BURST8_EN		(1 << 29)
 #define BM_APBH_CTRL0_APB_BURST_EN		(1 << 28)
-#define BP_APBH_CTRL0_CLKGATE_CHANNEL		8
 #define BP_APBH_CTRL0_RESET_CHANNEL		16
 #define HW_APBHX_CTRL1				0x010
 #define HW_APBHX_CTRL2				0x020
@@ -131,23 +130,6 @@ struct mxs_dma_engine {
 	struct mxs_dma_chan		mxs_chans[MXS_DMA_CHANNELS];
 };
 
-static inline void mxs_dma_clkgate(struct mxs_dma_chan *mxs_chan, int enable)
-{
-	struct mxs_dma_engine *mxs_dma = mxs_chan->mxs_dma;
-	int chan_id = mxs_chan->chan.chan_id;
-	int set_clr = enable ? MXS_CLR_ADDR : MXS_SET_ADDR;
-
-	/* enable apbh channel clock */
-	if (dma_is_apbh()) {
-		if (apbh_is_old())
-			writel(1 << (chan_id + BP_APBH_CTRL0_CLKGATE_CHANNEL),
-				mxs_dma->base + HW_APBHX_CTRL0 + set_clr);
-		else
-			writel(1 << chan_id,
-				mxs_dma->base + HW_APBHX_CTRL0 + set_clr);
-	}
-}
-
 static void mxs_dma_reset_chan(struct mxs_dma_chan *mxs_chan)
 {
 	struct mxs_dma_engine *mxs_dma = mxs_chan->mxs_dma;
@@ -166,9 +148,6 @@ static void mxs_dma_enable_chan(struct mxs_dma_chan *mxs_chan)
 	struct mxs_dma_engine *mxs_dma = mxs_chan->mxs_dma;
 	int chan_id = mxs_chan->chan.chan_id;
 
-	/* clkgate needs to be enabled before writing other registers */
-	mxs_dma_clkgate(mxs_chan, 1);
-
 	/* set cmd_addr up */
 	writel(mxs_chan->ccw_phys,
 		mxs_dma->base + HW_APBHX_CHn_NXTCMDAR(chan_id));
@@ -179,9 +158,6 @@ static void mxs_dma_enable_chan(struct mxs_dma_chan *mxs_chan)
 
 static void mxs_dma_disable_chan(struct mxs_dma_chan *mxs_chan)
 {
-	/* disable apbh channel clock */
-	mxs_dma_clkgate(mxs_chan, 0);
-
 	mxs_chan->status = DMA_SUCCESS;
 }
 
@@ -339,10 +315,7 @@ static int mxs_dma_alloc_chan_resources(struct dma_chan *chan)
 	if (ret)
 		goto err_clk;
 
-	/* clkgate needs to be enabled for reset to finish */
-	mxs_dma_clkgate(mxs_chan, 1);
 	mxs_dma_reset_chan(mxs_chan);
-	mxs_dma_clkgate(mxs_chan, 0);
 
 	dma_async_tx_descriptor_init(&mxs_chan->desc, chan);
 	mxs_chan->desc.tx_submit = mxs_dma_tx_submit;
@@ -542,8 +515,8 @@ static int mxs_dma_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
 
 	switch (cmd) {
 	case DMA_TERMINATE_ALL:
-		mxs_dma_disable_chan(mxs_chan);
 		mxs_dma_reset_chan(mxs_chan);
+		mxs_dma_disable_chan(mxs_chan);
 		break;
 	case DMA_PAUSE:
 		mxs_dma_pause_chan(mxs_chan);
-- 
1.5.6.5

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