Re: [PATCH] spi: Skip zero-length transfers in spi_transfer_one_message()

From: Mark Brown <broonie@kernel.org>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Robin Murphy <robin.murphy@arm.com>,
	Phil Elwell <phil@raspberrypi.com>,
	linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] spi: Skip zero-length transfers in spi_transfer_one_message()
Date: Fri, 12 Feb 2021 12:52:21 +0000	[thread overview]
Message-ID: <20210212125221.GD6057@sirena.org.uk> (raw)
In-Reply-To: <cd41a204107900c890b0234847fa0b62701f74cc.camel@suse.de>

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On Fri, Feb 12, 2021 at 01:48:21PM +0100, Nicolas Saenz Julienne wrote:
> On Fri, 2021-02-12 at 12:31 +0000, Mark Brown wrote:
> > On Thu, Feb 11, 2021 at 07:08:20PM +0100, Nicolas Saenz Julienne wrote:

> > > -		if (xfer->tx_buf || xfer->rx_buf) {
> > > +		if ((xfer->tx_buf || xfer->rx_buf) && xfer->len) {

> > I think the issue here is more that some users were passing in buffers
> > with zero length transfers, the above check was already intended to
> > catch this case but was working on the assumption that if there was
> > nothing to transfer then no buffer would be provided.

> Fair enough, maybe it makes sense to move the check into __spi_validate() and
> propagate an error upwards?

No, I think it's fine - there's probably some sensible use case with
drivers reusing a statically allocated transfer/buffer set for multiple
operations and just tweaking the length as needed which seems a bit
weird but I can't think of a reason not to allow it.  Your patch is
currently queued, all being well it'll get tested & pushed out later
today.

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