linux-kernel - Re: [PATCH for-next] arm64: defconfig: Set bcm2835-dma as built-in

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Message-Id: <C0400CAEQS8N.3P1J37PC0KU9F@linux-9qgx>
Date:   Fri, 24 Jan 2020 12:51:52 +0100
From:   "Nicolas Saenz Julienne" <nsaenzjulienne@...e.de>
To:     "Peter Ujfalusi" <peter.ujfalusi@...com>,
        "Ulf Hansson" <ulf.hansson@...aro.org>
Cc:     <f.fainelli@...il.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        <linux-kernel@...r.kernel.org>,
        <linux-rpi-kernel@...ts.infradead.org>,
        "Will Deacon" <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH for-next] arm64: defconfig: Set bcm2835-dma as built-in

Hi Peter,

On Fri Jan 24, 2020 at 1:31 PM, Peter Ujfalusi wrote:
> Hi Nicolas,
>
> On 24/01/2020 13.17, Nicolas Saenz Julienne wrote:
> > With the introduction of 738987a1d6f1 ("mmc: bcm2835: Use
> > dma_request_chan() instead dma_request_slave_channel()") sdhost-bcm2835
> > now waits for its DMA channel to be available when defined in the
> > device-tree (it would previously default to PIO). Albeit the right
> > behaviour, the MMC host is needed for booting. So this makes sure the
> > DMA channel shows up in time.
> > 
> > Fixes: 738987a1d6f1 ("mmc: bcm2835: Use dma_request_chan() instead dma_request_slave_channel()")
>
> it is not a bug, it is a feature ;)

Agree, I'm just afraid of your series being picked up by a stable
release without this patch. But maybe it's not necessary?

> Yes, if a driver have DMA binding and it is needed during boot then the
> DMA driver also needs to be built in.
> I believe it is desired to use DMA instead of PIO in any case for MMC
> and in the past bcm2835 did not used DMA if DMA was module and the MMC
> was built in.
>
> Sorry for the inconvenience this change has caused to bcm2835!

Not at all :)

> Reviewed-by: Peter Ujfalusi <peter.ujfalusi@...com>

Thanks,
Nicolas