linux-kernel - Re: [PATCH v4 1/7] dma: qcom: bam_dma: Fix command element mask field for BAM v1.6.0+

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Message-ID: <409c2e5f-1bf2-44ed-9c0f-df762320e068@kernel.org>
Date: Fri, 6 Feb 2026 18:12:00 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Md Sadre Alam <quic_mdalam@...cinc.com>, andersson@...nel.org,
 konradybcio@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, vkoul@...nel.org, Frank.Li@...nel.org,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Cc: quic_varada@...cinc.com
Subject: Re: [PATCH v4 1/7] dma: qcom: bam_dma: Fix command element mask field
 for BAM v1.6.0+

On 06/02/2026 11:01, Md Sadre Alam wrote:
> BAM version 1.6.0 and later changed the behavior of the mask field in
> command elements for read operations. In newer BAM versions, the mask
> field for read commands contains the upper 4 bits of the destination
> address to support 36-bit addressing, while for write commands it
> continues to function as a traditional write mask.
> 
> This change causes NAND enumeration failures on platforms like IPQ5424

Please do not use "This commit/patch/change", but imperative mood. See
longer explanation here:
https://elixir.bootlin.com/linux/v6.16/source/Documentation/process/submitting-patches.rst#L94

> that use BAM v1.6.0+, because the current code sets mask=0xffffffff
> for all commands. For read commands on newer BAM versions, this results
> in the hardware interpreting the destination address as 0xf_xxxxxxxx
> (invalid high memory) instead of the intended 0x0_xxxxxxxx address.
> 
> Fixed this issue by:
> 1. Updating the bam_cmd_element structure documentation to reflect the
>    dual purpose of the mask field
> 2. Modifying bam_prep_ce_le32() to set appropriate mask values based on
>    command type:
>    - For read commands: mask = 0 (32-bit addressing, upper bits = 0)
>    - For write commands: mask = 0xffffffff (traditional write mask)
> 3. Maintaining backward compatibility with older BAM versions
> 
> This fix enables proper NAND functionality on IPQ5424 and other platforms
> using BAM v1.6.0+ while preserving compatibility with existing systems.

Fixes tag? CC-stable?

Why is this part of DTS patchset? Do not combine independent work, you
only make it difficult for maintainers to handle your work.


Best regards,
Krzysztof