linux-kernel - [PATCH v3] dmaengine: qcom: bam_dma: Avoid writing unavailable register

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Message-ID: <20241209073143.3413552-1-quic_mdalam@quicinc.com>
Date: Mon, 9 Dec 2024 13:01:43 +0530
From: Md Sadre Alam <quic_mdalam@...cinc.com>
To: <vkoul@...nel.org>, <martin.petersen@...cle.com>, <ulf.hansson@...aro.org>,
        <av2082000@...il.com>, <linux-arm-msm@...r.kernel.org>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <uic_mdalam@...cinc.com>, <quic_srichara@...cinc.com>,
        <quic_varada@...cinc.com>
Subject: [PATCH v3] dmaengine: qcom: bam_dma: Avoid writing unavailable register

Avoid writing unavailable register in BAM-Lite mode.
BAM_DESC_CNT_TRSHLD register is unavailable in BAM-Lite
mode. Its only available in BAM-NDP mode. So only write
this register for clients who is using BAM-NDP.

Signed-off-by: Md Sadre Alam <quic_mdalam@...cinc.com>
---

Change in [v3]

* Removed BAM_LITE macro

* Updated commit message

* Adjusted if condition check

* Renamed BAM-NDP macro to BAM_NDP_REVISION_START and 
  BAM_NDP_REVISION_END

Change in [v2]

* Replace 0xff with REVISION_MASK in the statement
  bdev->bam_revision = val & REVISION_MASK

Change in [v1]

* Added initial patch

 drivers/dma/qcom/bam_dma.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
index d43a881e43b9..a00dd0331ff5 100644
--- a/drivers/dma/qcom/bam_dma.c
+++ b/drivers/dma/qcom/bam_dma.c
@@ -59,6 +59,9 @@ struct bam_desc_hw {
 #define DESC_FLAG_NWD BIT(12)
 #define DESC_FLAG_CMD BIT(11)
 
+#define BAM_NDP_REVISION_START	0x20
+#define BAM_NDP_REVISION_END	0x27
+
 struct bam_async_desc {
 	struct virt_dma_desc vd;
 
@@ -398,6 +401,7 @@ struct bam_device {
 
 	/* dma start transaction tasklet */
 	struct tasklet_struct task;
+	u32 bam_revision;
 };
 
 /**
@@ -441,8 +445,10 @@ static void bam_reset(struct bam_device *bdev)
 	writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
 
 	/* set descriptor threshold, start with 4 bytes */
-	writel_relaxed(DEFAULT_CNT_THRSHLD,
-			bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
+	if (bdev->bam_revision >= BAM_NDP_REVISION_START &&
+	    bdev->bam_revision <= BAM_NDP_REVISION_END)
+		writel_relaxed(DEFAULT_CNT_THRSHLD,
+			       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
 
 	/* Enable default set of h/w workarounds, ie all except BAM_FULL_PIPE */
 	writel_relaxed(BAM_CNFG_BITS_DEFAULT, bam_addr(bdev, 0, BAM_CNFG_BITS));
@@ -1000,9 +1006,10 @@ static void bam_apply_new_config(struct bam_chan *bchan,
 			maxburst = bchan->slave.src_maxburst;
 		else
 			maxburst = bchan->slave.dst_maxburst;
-
-		writel_relaxed(maxburst,
-			       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
+		if (bdev->bam_revision >= BAM_NDP_REVISION_START &&
+		    bdev->bam_revision <= BAM_NDP_REVISION_END)
+			writel_relaxed(maxburst,
+				       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
 	}
 
 	bchan->reconfigure = 0;
@@ -1192,10 +1199,11 @@ static int bam_init(struct bam_device *bdev)
 	u32 val;
 
 	/* read revision and configuration information */
-	if (!bdev->num_ees) {
-		val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
+	val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
+	if (!bdev->num_ees)
 		bdev->num_ees = (val >> NUM_EES_SHIFT) & NUM_EES_MASK;
-	}
+
+	bdev->bam_revision = val & REVISION_MASK;
 
 	/* check that configured EE is within range */
 	if (bdev->ee >= bdev->num_ees)
-- 
2.34.1