Re: [PATCH v4] dmaengine: qcom: bam_dma: Avoid writing unavailable register

[Georgi Djakov <djakov@kernel.org>]

On 20.12.24 11:42, 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 only write
> this register for clients who is using BAM-NDP.
> 
> Signed-off-by: Md Sadre Alam <quic_mdalam@quicinc.com>
> ---

My Dragonboard db845c fails to boot on recent linux-next releases and
git bisect points to this patch. It boots again when it's reverted.

[..]

>   
>   	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;

The problem seems to occur when we try to read the revision for the
slimbus bam instance at 0x17184000 (which has "qcom,num-ees = <2>;").

Thanks,
Georgi