linux-kernel - RE: [PATCH 1/2] arm64: dts: imx8mn: Add spba1 bus

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Date:   Tue, 11 May 2021 12:20:42 +0000
From:   Robin Gong <yibin.gong@....com>
To:     Adam Ford <aford173@...il.com>, Shawn Guo <shawnguo@...nel.org>
CC:     arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] arm64: dts: imx8mn: Add spba1 bus

On 2021/05/11 18:45 Adam Ford <aford173@...il.com> wrote:
> > Also may I ask if you have a real use case for this bus node?
> 
> The reference manual shows the SPBA bus tells the DMA controller which
> peripherals are associated with it.  Nearly all the i.MX boards use this.  The
> boards I support have Bluetooth devices connected to a UART running high
> speeds, and if the DMA driver isn't loaded, I can see a performance change.
Compare PIO with DMA on UART, but not w/o this  'spba bus node ' patch? 

> In fact, if the DMA firmware isn't loaded, I often get transfer errors.
UART use SDMA ROM firmware instead of RAM firmware, so it should work
even without sdma RAM firmware loaded.  Still curious what really happen in
your board without this patch.