linux-kernel - Re: [PATCH] ARM: dts: gta04: fix excess dma channel usage

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Date:   Mon, 27 Mar 2023 11:13:27 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     bcousson@...libre.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, aford173@...il.com,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "H. Nikolaus Schaller" <hns@...delico.com>
Subject: Re: [PATCH] ARM: dts: gta04: fix excess dma channel usage

* Andreas Kemnade <andreas@...nade.info> [230113 23:12]:
> From: "H. Nikolaus Schaller" <hns@...delico.com>
> 
> OMAP processors support 32 channels but there is no check or
> inspect this except booting a device and looking at dmesg reports
> of not available channels.
> 
> Recently some more subsystems with DMA (aes1+2) were added filling
> the list of dma channels beyond the limit of 32 (even if other
> parameters indicate 96 or 128 channels). This leads to random
> subsystem failures i(e.g. mcbsp for audio) after boot or boot
> messages that DMA can not be initialized.
> 
> Another symptom is that
> 
> /sys/kernel/debug/dmaengine/summary
> 
> has 32 entries and does not show all required channels.
> 
> Fix by disabling unused (on the GTA04 hardware) mcspi1...4.
> Each SPI channel allocates 4 DMA channels rapidly filling
> the available ones.
> 
> Disabling unused SPI modules on the OMAP3 SoC may also save
> some energy (has not been checked).

Applying this into omap-for-v6.4/dt based on what we discussed
in this thread earlier.

Thanks,

Tony