linux-kernel - Re: [PATCH v1] dmaengine: tegra-apb: Error out if DMA_PREP

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Date:   Thu, 30 May 2019 13:01:35 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Vinod Koul <vkoul@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Ben Dooks <ben.dooks@...ethink.co.uk>
CC:     <dmaengine@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] dmaengine: tegra-apb: Error out if DMA_PREP_INTERRUPT
 flag is unset


On 29/05/2019 22:43, Dmitry Osipenko wrote:
> Apparently driver was never tested with DMA_PREP_INTERRUPT flag being
> unset since it completely disables interrupt handling instead of skipping
> the callbacks invocations, hence putting channel into unusable state.
> 
> The flag is always set by all of kernel drivers that use APB DMA, so let's
> error out in otherwise case for consistency. It won't be difficult to
> support that case properly if ever will be needed.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/dma/tegra20-apb-dma.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index cf462b1abc0b..2c84a660ba36 100644
> --- a/drivers/dma/tegra20-apb-dma.c
> +++ b/drivers/dma/tegra20-apb-dma.c
> @@ -988,8 +988,12 @@ static struct dma_async_tx_descriptor *tegra_dma_prep_slave_sg(
>  		csr |= tdc->slave_id << TEGRA_APBDMA_CSR_REQ_SEL_SHIFT;
>  	}
>  
> -	if (flags & DMA_PREP_INTERRUPT)
> +	if (flags & DMA_PREP_INTERRUPT) {
>  		csr |= TEGRA_APBDMA_CSR_IE_EOC;
> +	} else {
> +		WARN_ON_ONCE(1);
> +		return NULL;
> +	}
>  
>  	apb_seq |= TEGRA_APBDMA_APBSEQ_WRAP_WORD_1;
>  
> @@ -1131,8 +1135,12 @@ static struct dma_async_tx_descriptor *tegra_dma_prep_dma_cyclic(
>  		csr |= tdc->slave_id << TEGRA_APBDMA_CSR_REQ_SEL_SHIFT;
>  	}
>  
> -	if (flags & DMA_PREP_INTERRUPT)
> +	if (flags & DMA_PREP_INTERRUPT) {
>  		csr |= TEGRA_APBDMA_CSR_IE_EOC;
> +	} else {
> +		WARN_ON_ONCE(1);
> +		return NULL;
> +	}
>  
>  	apb_seq |= TEGRA_APBDMA_APBSEQ_WRAP_WORD_1;

Looks good to me.

Acked-by: Jon Hunter <jonathanh@...dia.com>

Cheers
Jon

-- 
nvpublic