Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash devices

From: Mark Brown <broonie@kernel.org>
To: Vignesh R <vigneshr@ti.com>
Cc: Tony Lindgren <tony@atomide.com>,
	Michal Suchanek <hramrach@gmail.com>,
	Russell King <linux@arm.linux.org.uk>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-mtd@lists.infradead.org, linux-spi@vger.kernel.org
Subject: Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash devices
Date: Wed, 4 Nov 2015 14:39:15 +0000	[thread overview]
Message-ID: <20151104143915.GI1717@sirena.org.uk> (raw)
In-Reply-To: <1446545174-14193-2-git-send-email-vigneshr@ti.com>

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On Tue, Nov 03, 2015 at 03:36:10PM +0530, Vignesh R wrote:

> +	}
> +	mutex_lock(&master->mmap_lock_mutex);
> +	ret = master->spi_mtd_mmap_read(spi, from, len, retlen, buf,
> +					read_opcode, addr_width,
> +					dummy_bytes);
> +	mutex_unlock(&master->mmap_lock_mutex);
> +	if (master->auto_runtime_pm)
> +		pm_runtime_put(master->dev.parent);

It's a bit worrying that this doesn't sync with the message queue except
via the mutex: this means that we might be out of order with respect to
any asynchronous transfers that are happening on the device.  I'm not
sure that this is a practical problem, though there is some risk of
unfair scheduling that would have to be under extreme load and it might
make sense to prioritise reads anyway.

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