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

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Message-ID: <Z0Fb5xBolEtwyUKb@hu-varada-blr.qualcomm.com>
Date: Sat, 23 Nov 2024 10:06:55 +0530
From: Varadarajan Narayanan <quic_varada@...cinc.com>
To: Md Sadre Alam <quic_mdalam@...cinc.com>
CC: <vkoul@...nel.org>, <ulf.hansson@...aro.org>, <martin.petersen@...cle.com>,
        <kees@...nel.org>, <dave.jiang@...el.com>, <av2082000@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_srichara@...cinc.com>
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Avoid writing unavailable
 register

On Fri, Nov 22, 2024 at 12:46:49PM +0530, Md Sadre Alam wrote:
> 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 avoid writing
> this register for clients who is using BAM-Lite mode.
>
> Signed-off-by: Md Sadre Alam <quic_mdalam@...cinc.com>
> ---
>  drivers/dma/qcom/bam_dma.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> index d43a881e43b9..13a08c03746b 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_LITE	0x13
> +#define BAM_NDP		0x20
> +
>  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 +445,9 @@ 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_LITE && bdev->bam_revision < BAM_NDP)
> +		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 +1005,9 @@ 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_LITE && bdev->bam_revision < BAM_NDP)
> +			writel_relaxed(maxburst,
> +				       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
>  	}
>
>  	bchan->reconfigure = 0;
> @@ -1192,10 +1197,11 @@ 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 & 0xff;

Use REVISION_MASK instead of 0xff

-Varada

>  	/* check that configured EE is within range */
>  	if (bdev->ee >= bdev->num_ees)
> --
> 2.34.1
>