linux-kernel - Re: [PATCH v5 08/10] spi: expose master transfer size limitation.

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Message-ID: <20151201195816.GS1929@sirena.org.uk>
Date:	Tue, 1 Dec 2015 19:58:16 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Heiner Kallweit <hkallweit1@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Han Xu <han.xu@...escale.com>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Stephen Warren <swarren@...dia.com>,
	"Andrew F. Davis" <afd@...com>, Marek Vasut <marex@...x.de>,
	Rafał Miłecki <zajec5@...il.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Gabor Juhos <juhosg@...nwrt.org>,
	Bean Huo 霍斌斌 <beanhuo@...ron.com>,
	Furquan Shaikh <furquan@...gle.com>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-spi@...r.kernel.org
Subject: Re: [PATCH v5 08/10] spi: expose master transfer size limitation.

On Tue, Dec 01, 2015 at 04:51:06PM -0000, Michal Suchanek wrote:
> On some SPI controllers it is not feasible to transfer arbitrary amount
> of data at once.
> 
> When the limit on transfer size is a few kilobytes at least it makes
> sense to use the SPI hardware rather than reverting to gpio driver.

> +	/*
> +	 * on some hardware transfer size may be constrained
> +	 * the limit may depend on device transfer settings
> +	 */
> +	size_t (*max_transfer_size)(struct spi_device *spi);

Heiner submitted a *very* similar patch just now with a straight
variable plus accessor instead of a function and using a name with _msg.
I'm ambivalent on the implementation but prefer the naming here since
that's more the limitation we're trying to express I think (some
hardware does have limiations about multple transfers too).  Can the two
of you come up with something that works for both of you?

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