From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753395AbcLJRgi (ORCPT ); Sat, 10 Dec 2016 12:36:38 -0500 Received: from saturn.retrosnub.co.uk ([178.18.118.26]:48598 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751039AbcLJRgh (ORCPT ); Sat, 10 Dec 2016 12:36:37 -0500 Subject: Re: [PATCH] iio: adc: max1027: allocate DMA-safe buffer To: Marcus Folkesson , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Matt Ranostay , Sandhya Bankar References: <20161209102435.30638-1-marcus.folkesson@gmail.com> Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org From: Jonathan Cameron Message-ID: <915bf030-49c3-5d56-73c2-9c3da3f1a02e@kernel.org> Date: Sat, 10 Dec 2016 17:36:34 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20161209102435.30638-1-marcus.folkesson@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/12/16 10:24, Marcus Folkesson wrote: > The buffer needs to be DMA-safe when used with spi_read() > > Signed-off-by: Marcus Folkesson Please read the documentation in include/linux/gfp.h about GFP_DMA. Specifically: 220 * GFP_DMA exists for historical reasons and should be avoided where possible. 221 * The flags indicates that the caller requires that the lowest zone be 222 * used (ZONE_DMA or 16M on x86-64). Ideally, this would be removed but 223 * it would require careful auditing as some users really require it and 224 * others use the flag to avoid lowmem reserves in ZONE_DMA and treat the 225 * lowest zone as a type of emergency reserve. Seems unlikely this applies! This caught me by surprise as I didn't even know that flag existed - hence I went digging. Jonathan > --- > drivers/iio/adc/max1027.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c > index 712fbd2b1f16..ff1f1f15a873 100644 > --- a/drivers/iio/adc/max1027.c > +++ b/drivers/iio/adc/max1027.c > @@ -435,7 +435,7 @@ static int max1027_probe(struct spi_device *spi) > > st->buffer = devm_kmalloc(&indio_dev->dev, > indio_dev->num_channels * 2, > - GFP_KERNEL); > + GFP_KERNEL | GFP_DMA); > if (st->buffer == NULL) { > dev_err(&indio_dev->dev, "Can't allocate buffer\n"); > return -ENOMEM; >