linux-kernel - Re: [PATCH v4 09/14] mmc: omap_hsmmc: set max

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Date:	Fri, 11 Jan 2013 09:53:30 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Matt Porter <mporter@...com>
Cc:	Sekhar Nori <nsekhar@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Benoit Cousson <b-cousson@...com>,
	Russell King <linux@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>,
	Rob Landley <rob@...dley.net>, Chris Ball <cjb@...top.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>,
	Arnd Bergmann <arnd@...db.de>, Dan Williams <djbw@...com>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH v4 09/14] mmc: omap_hsmmc: set max_segs based on dma
 engine limitations

* Matt Porter <mporter@...com> [130110 21:47]:
> The EDMA DMAC has a hardware limitation that prevents supporting
> scatter gather lists with any number of segments. The DMA Engine
> API reports the maximum number of segments a channel can support
> via the optional dma_get_channel_caps() API. If the nr_segs
> capability is present, the value is used to configure mmc->max_segs
> appropriately.

Acked-by: Tony Lindgren <tony@...mide.com>
 
> Signed-off-by: Matt Porter <mporter@...com>
> ---
>  drivers/mmc/host/omap_hsmmc.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index e79b12d..f74bd69 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -1769,6 +1769,7 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  	const struct of_device_id *match;
>  	dma_cap_mask_t mask;
>  	unsigned tx_req, rx_req;
> +	struct dmaengine_chan_caps *dma_chan_caps;
>  	struct pinctrl *pinctrl;
>  
>  	match = of_match_device(of_match_ptr(omap_mmc_of_match), &pdev->dev);
> @@ -1935,6 +1936,11 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  		goto err_irq;
>  	}
>  
> +	/* Some DMA Engines only handle a limited number of SG segments */
> +	dma_chan_caps = dma_get_channel_caps(host->rx_chan, DMA_DEV_TO_MEM);
> +	if (dma_chan_caps && dma_chan_caps->seg_nr)
> +		mmc->max_segs = dma_chan_caps->seg_nr;
> +
>  	/* Request IRQ for MMC operations */
>  	ret = request_irq(host->irq, omap_hsmmc_irq, 0,
>  			mmc_hostname(mmc), host);
> -- 
> 1.7.9.5
> 
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