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From:   Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
To:     vkoul@kernel.org
Cc:     dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, sricharan@codeaurora.org,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Subject: [PATCH] dmaengine: qcom-bam: fix circular buffer handling
Date:   Fri, 14 Jun 2019 15:20:12 +0100
Message-Id: <20190614142012.31384-1-srinivas.kandagatla@linaro.org>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

For some reason arguments to most of the circular buffers
macros are used in reverse, tail is used for head and vice versa.

This leads to bam thinking that there is an extra descriptor at the
end and leading to retransmitting descriptor which was not scheduled
by any driver. This happens after MAX_DESCRIPTORS (4096) are scheduled
and done, so most of the drivers would not notice this, unless they are
heavily using bam dma. Originally found this issue while testing
SoundWire over SlimBus on DB845c which uses DMA very heavily for
read/writes.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---
 drivers/dma/qcom/bam_dma.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index cb860cb53c27..43d7b0a9713a 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -350,8 +350,8 @@ static const struct reg_offset_data bam_v1_7_reg_info[] = {
 #define BAM_DESC_FIFO_SIZE	SZ_32K
 #define MAX_DESCRIPTORS (BAM_DESC_FIFO_SIZE / sizeof(struct bam_desc_hw) - 1)
 #define BAM_FIFO_SIZE	(SZ_32K - 8)
-#define IS_BUSY(chan)	(CIRC_SPACE(bchan->tail, bchan->head,\
-			 MAX_DESCRIPTORS + 1) == 0)
+#define IS_BUSY(chan)	(CIRC_SPACE(bchan->head, bchan->tail,\
+			 MAX_DESCRIPTORS) == 0)
 
 struct bam_chan {
 	struct virt_dma_chan vc;
@@ -806,7 +806,7 @@ static u32 process_channel_irqs(struct bam_device *bdev)
 		offset /= sizeof(struct bam_desc_hw);
 
 		/* Number of bytes available to read */
-		avail = CIRC_CNT(offset, bchan->head, MAX_DESCRIPTORS + 1);
+		avail = CIRC_CNT(bchan->head, offset, MAX_DESCRIPTORS);
 
 		list_for_each_entry_safe(async_desc, tmp,
 					 &bchan->desc_list, desc_node) {
@@ -997,8 +997,7 @@ static void bam_start_dma(struct bam_chan *bchan)
 			bam_apply_new_config(bchan, async_desc->dir);
 
 		desc = async_desc->curr_desc;
-		avail = CIRC_SPACE(bchan->tail, bchan->head,
-				   MAX_DESCRIPTORS + 1);
+		avail = CIRC_SPACE(bchan->head, bchan->tail, MAX_DESCRIPTORS);
 
 		if (async_desc->num_desc > avail)
 			async_desc->xfer_len = avail;
-- 
2.21.0