From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14A53C282E1 for ; Mon, 22 Apr 2019 08:56:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2016206A3 for ; Mon, 22 Apr 2019 08:56:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727141AbfDVI4c (ORCPT ); Mon, 22 Apr 2019 04:56:32 -0400 Received: from saturn.retrosnub.co.uk ([46.235.226.198]:41722 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725914AbfDVI4c (ORCPT ); Mon, 22 Apr 2019 04:56:32 -0400 Received: from archlinux (cpc91196-cmbg18-2-0-cust659.5-4.cable.virginm.net [81.96.234.148]) by saturn.retrosnub.co.uk (Postfix; Retrosnub mail submission) with ESMTPSA id EB1D69E8C5F; Mon, 22 Apr 2019 09:56:29 +0100 (BST) Date: Mon, 22 Apr 2019 09:56:27 +0100 From: Jonathan Cameron To: Alexandru Ardelean Cc: , Lars-Peter Clausen Subject: Re: [PATCH V2] iio: ad_sigma_delta: Don't put SPI transfer buffer on the stack Message-ID: <20190422095627.4d115944@archlinux> In-Reply-To: <20190416081916.26287-1-alexandru.ardelean@analog.com> References: <20190409075821.26104-1-alexandru.ardelean@analog.com> <20190416081916.26287-1-alexandru.ardelean@analog.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-iio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On Tue, 16 Apr 2019 11:19:16 +0300 Alexandru Ardelean wrote: > From: Lars-Peter Clausen > > Use a heap allocated memory for the SPI transfer buffer. Using stack memory > will not work on some architectures when using DMA. > > This also avoids potential stack corruption, as it makes sure that the > buffer is in it's own cacheline and (obviously) not on the stack. > > Fixes: af3008485ea03 ("iio:adc: Add common code for ADI Sigma Delta devices") > Signed-off-by: Lars-Peter Clausen > Signed-off-by: Alexandru Ardelean Hi Alex, Thanks for the update. I'm unclear why we can't just use one large buffer for both cases? i.e put the reg_data usecases in the buf_data buffer (renamed). Jonathan > --- > Changelog v1 -> v2: > * added ____cacheline_aligned to `buf_data` > * extended comment about cacheline > * added fixes tag > > drivers/iio/adc/ad_sigma_delta.c | 22 +++++++++++----------- > include/linux/iio/adc/ad_sigma_delta.h | 3 ++- > 2 files changed, 13 insertions(+), 12 deletions(-) > > diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c > index af6cbc683214..02d9049b9218 100644 > --- a/drivers/iio/adc/ad_sigma_delta.c > +++ b/drivers/iio/adc/ad_sigma_delta.c > @@ -58,7 +58,7 @@ EXPORT_SYMBOL_GPL(ad_sd_set_comm); > int ad_sd_write_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg, > unsigned int size, unsigned int val) > { > - uint8_t *data = sigma_delta->data; > + uint8_t *data = sigma_delta->reg_data; > struct spi_transfer t = { > .tx_buf = data, > .len = size + 1, > @@ -102,7 +102,7 @@ EXPORT_SYMBOL_GPL(ad_sd_write_reg); > static int ad_sd_read_reg_raw(struct ad_sigma_delta *sigma_delta, > unsigned int reg, unsigned int size, uint8_t *val) > { > - uint8_t *data = sigma_delta->data; > + uint8_t *data = sigma_delta->reg_data; > int ret; > struct spi_transfer t[] = { > { > @@ -148,24 +148,24 @@ int ad_sd_read_reg(struct ad_sigma_delta *sigma_delta, > { > int ret; > > - ret = ad_sd_read_reg_raw(sigma_delta, reg, size, sigma_delta->data); > + ret = ad_sd_read_reg_raw(sigma_delta, reg, size, sigma_delta->reg_data); > if (ret < 0) > goto out; > > switch (size) { > case 4: > - *val = get_unaligned_be32(sigma_delta->data); > + *val = get_unaligned_be32(sigma_delta->reg_data); > break; > case 3: > - *val = (sigma_delta->data[0] << 16) | > - (sigma_delta->data[1] << 8) | > - sigma_delta->data[2]; > + *val = (sigma_delta->reg_data[0] << 16) | > + (sigma_delta->reg_data[1] << 8) | > + sigma_delta->reg_data[2]; > break; > case 2: > - *val = get_unaligned_be16(sigma_delta->data); > + *val = get_unaligned_be16(sigma_delta->reg_data); > break; > case 1: > - *val = sigma_delta->data[0]; > + *val = sigma_delta->reg_data[0]; > break; > default: > ret = -EINVAL; > @@ -403,12 +403,12 @@ static irqreturn_t ad_sd_trigger_handler(int irq, void *p) > struct iio_poll_func *pf = p; > struct iio_dev *indio_dev = pf->indio_dev; > struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev); > + uint8_t *data = sigma_delta->buf_data; > unsigned int reg_size; > unsigned int data_reg; > - uint8_t data[16]; > int ret; > > - memset(data, 0x00, 16); > + memset(sigma_delta->buf_data, 0x00, sizeof(sigma_delta->buf_data)); > > reg_size = indio_dev->channels[0].scan_type.realbits + > indio_dev->channels[0].scan_type.shift; > diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h > index 6e9fb1932dde..d95216ce8a94 100644 > --- a/include/linux/iio/adc/ad_sigma_delta.h > +++ b/include/linux/iio/adc/ad_sigma_delta.h > @@ -79,7 +79,8 @@ struct ad_sigma_delta { > * DMA (thus cache coherency maintenance) requires the > * transfer buffers to live in their own cache lines. > */ > - uint8_t data[4] ____cacheline_aligned; > + uint8_t reg_data[4] ____cacheline_aligned; > + uint8_t buf_data[16] ____cacheline_aligned; The usual assumption is that a device is safe against itself, so we can't get cacheline corruption in a single action from the device to itself. This does make me wonder why we have two buffers like this at all though! > }; > > static inline int ad_sigma_delta_set_channel(struct ad_sigma_delta *sd,