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

[Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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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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