linux-kernel - Re: [PATCH v3 1/3] mmc: sdhci: Set DMA mask when adding host

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Message-ID: <2562091.6cJRuD3dK9@wuerfel>
Date:	Fri, 04 Mar 2016 16:57:15 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	gnurou@...il.com
Subject: Re: [PATCH v3 1/3] mmc: sdhci: Set DMA mask when adding host

On Friday 04 March 2016 19:38:43 Alexandre Courbot wrote:
> Set the DMA mask in sdhci_add_host() after we determined the
> capabilities of the device. 64-bit devices in particular are given the
> proper mask that ensures bounce buffers are not used.
> 
> Also disable DMA if no proper DMA mask can be set, as the DMA-API
> documentation specifies.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  drivers/mmc/host/sdhci.c | 46 +++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index fd9139947fa3..00fb45ba6f39 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2857,6 +2857,34 @@ struct sdhci_host *sdhci_alloc_host(struct device *dev,
>  
>  EXPORT_SYMBOL_GPL(sdhci_alloc_host);
>  
> +static int sdhci_set_dma_mask(struct sdhci_host *host)
> +{
> +	struct mmc_host *mmc = host->mmc;
> +	struct device *dev = mmc_dev(mmc);
> +	int ret = -EINVAL;
> +
> +	if (host->quirks2 & SDHCI_QUIRK2_BROKEN_64_BIT_DMA)
> +		host->flags &= ~SDHCI_USE_64_BIT_DMA;
> +
> +	/* Try 64-bit mask if hardware is capable  of it */
> +	if (host->flags & SDHCI_USE_64_BIT_DMA) {
> +		ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
> +		if (ret)
> +			pr_warn("%s: Failed to set 64-bit DMA mask.\n",
> +				mmc_hostname(mmc));
> +	}
> +

I think you need to disable the SDHCI_USE_64_BIT_DMA flag when
dma_set_mask_and_coherent() fails here. Otherwise looks good.

	Arnd