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

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Date:   Fri, 24 Jan 2020 13:31:14 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     <f.fainelli@...il.com>, <linux-rpi-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH for-next] arm64: defconfig: Set bcm2835-dma as built-in

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 ;)

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!

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

> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> ---
>  arch/arm64/configs/defconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
> index 4631a1190719..905109f6814f 100644
> --- a/arch/arm64/configs/defconfig
> +++ b/arch/arm64/configs/defconfig
> @@ -683,7 +683,7 @@ CONFIG_RTC_DRV_SNVS=m
>  CONFIG_RTC_DRV_IMX_SC=m
>  CONFIG_RTC_DRV_XGENE=y
>  CONFIG_DMADEVICES=y
> -CONFIG_DMA_BCM2835=m
> +CONFIG_DMA_BCM2835=y
>  CONFIG_DMA_SUN6I=m
>  CONFIG_FSL_EDMA=y
>  CONFIG_IMX_SDMA=y
> 

- Péter

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