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From:   Adam Ford <aford173@gmail.com>
Date:   Tue, 11 May 2021 09:48:38 -0500
Message-ID: <CAHCN7xJ5Hq6bRpEgE8Pi9VbQ_Kejy-sgKQsJ93pQEG3U_Wsu=Q@mail.gmail.com>
Subject: Re: [PATCH 1/2] arm64: dts: imx8mn: Add spba1 bus
To:     Robin Gong <yibin.gong@nxp.com>
Cc:     Shawn Guo <shawnguo@kernel.org>,
        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>
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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.

adam
>
>
>
>