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Date:   Thu, 13 May 2021 10:09:00 +0800
From:   Shawn Guo <shawnguo@kernel.org>
To:     Adam Ford <aford173@gmail.com>
Cc:     Robin Gong <yibin.gong@nxp.com>,
        arm-soc <linux-arm-kernel@lists.infradead.org>,
        Rob Herring <robh+dt@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        dl-linux-imx <linux-imx@nxp.com>,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] arm64: dts: imx8mn: Add spba1 bus
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On Tue, May 11, 2021 at 09:48:38AM -0500, Adam Ford wrote:
> On Tue, May 11, 2021 at 7:20 AM Robin Gong <yibin.gong@nxp.com> wrote:
> >
> > On 2021/05/11 18:45 Adam Ford <aford173@gmail.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.
> 
> What I am seeing is that at times, the HCI UART loading before the DMA
> firmware is loaded.
> 
> [   10.582037] Bluetooth: HCI UART driver ver 2.3
> [   10.586867] Bluetooth: HCI UART protocol H4 registered
> [   10.593566] imx-sdma 30bd0000.dma-controller: sdma firmware not ready!
> [   10.594548] Bluetooth: HCI UART protocol Broadcom registered
> [   10.600108] imx-uart 30860000.serial: We cannot prepare for the RX slave dma!
> 
> When I get the above message, the bluetooth chip I have throws
> timeouts and does not function.
> 
> [   10.615090] imx-sdma 302c0000.dma-controller: loaded firmware 4.5
> 
> Once the firmware is loaded, I can unload the HCI Uart driver and
> re-load Bluetooth works again.
> 
> Based on that, I've been having my system delay the loading of the
> Bluetooth modules until after the firmware is loaded, but this tells
> me there is a relationship between the DMA and UART.

Yeah, I can see how DMA firmware impacts your Bluetooth device, but do
not follow how this spba node change make a difference here.

Nevertheless, patches look good.  Applied, thanks.

Shawn