From: Oliver Neukum <oneukum@suse.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Oliver Neukum <oneukum@suse.com>
Cc: Ye Xiang <xiang.ye@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Arnd Bergmann <arnd@arndb.de>,
Matthias Kaehlcke <mka@chromium.org>, Lee Jones <lee@kernel.org>,
Wolfram Sang <wsa@kernel.org>, Tyrone Ting <kfting@nuvoton.com>,
Mark Brown <broonie@kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <brgl@bgdev.pl>,
linux-usb@vger.kernel.org, linux-i2c@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org,
linux-gpio@vger.kernel.org, srinivas.pandruvada@intel.com,
heikki.krogerus@linux.intel.com, sakari.ailus@linux.intel.com,
zhifeng.wang@intel.com, wentong.wu@intel.com,
lixu.zhang@intel.com
Subject: Re: [PATCH v4 2/5] gpio: Add support for Intel LJCA USB GPIO driver
Date: Thu, 9 Mar 2023 18:30:53 +0100 [thread overview]
Message-ID: <5b34408d-8589-d735-9a77-a651ea661e01@suse.com> (raw)
In-Reply-To: <ZAnku01goVDCuNM+@smile.fi.intel.com>
On 09.03.23 14:52, Andy Shevchenko wrote:
> On Thu, Mar 09, 2023 at 02:40:10PM +0100, Oliver Neukum wrote:
>> On 09.03.23 08:10, Ye Xiang wrote:
>>> + u8 obuf[LJCA_GPIO_BUF_SIZE];
>>> + u8 ibuf[LJCA_GPIO_BUF_SIZE];
>>
>> And here we have a violation of DMA coherency rules.
>> Basically you cannot embed buffers into other data structures
>> if they can be subject to DMA.
>
> Huh?!
>
> The problem here is alignment. But other than that I can't see the issue with
> embedding into structures the instances of which will be allocated on the heap.
Hi,
These constraints are documented in dma-api-howto, but perhaps this
is inconvenient to read through.
Let me explain for the input case. On certain CPUs DMA does not
update CPU caches. Hence when you want to read data generated by DMA
you must read from RAM. Hence you invalidate the cache line with dma_map_*
operations.
Those cache lines must stay invalidated. If you wish to guarantee that,
you cannot access a data structure that shares a cache line with a buffer,
until you are sure that DMA is finished.
On the affected architectures kmalloc() makes sure that no allocation straddles
cache lines.
Regards
Oliver
next prev parent reply other threads:[~2023-03-09 17:31 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-09 7:10 [PATCH v4 0/5] Add Intel LJCA device driver Ye Xiang
2023-03-09 7:10 ` [PATCH v4 1/5] mfd: Add support for Intel LJCA device Ye Xiang
2023-03-09 7:49 ` Greg Kroah-Hartman
2023-03-09 9:10 ` Ye, Xiang
2023-03-09 9:26 ` Greg Kroah-Hartman
2023-03-09 10:16 ` Ye, Xiang
2023-03-09 7:52 ` Greg Kroah-Hartman
2023-03-09 9:31 ` Ye, Xiang
2023-03-09 9:41 ` Greg Kroah-Hartman
2023-03-09 10:06 ` Andi Shyti
2023-03-09 15:45 ` Ye, Xiang
2023-03-09 15:58 ` Greg Kroah-Hartman
2023-03-09 17:42 ` Ye, Xiang
2023-03-09 7:56 ` Arnd Bergmann
2023-03-09 10:00 ` Ye, Xiang
2023-03-09 11:03 ` Mark Brown
2023-03-09 11:30 ` Arnd Bergmann
2023-03-09 12:53 ` Oliver Neukum
2023-03-10 4:14 ` Ye, Xiang
2023-03-13 13:27 ` Oliver Neukum
2023-03-14 7:15 ` Ye, Xiang
2023-03-09 7:10 ` [PATCH v4 2/5] gpio: Add support for Intel LJCA USB GPIO driver Ye Xiang
2023-03-09 13:40 ` Oliver Neukum
2023-03-09 13:52 ` Andy Shevchenko
2023-03-09 14:06 ` Greg Kroah-Hartman
2023-03-09 14:18 ` Linus Walleij
2023-03-09 14:36 ` Greg Kroah-Hartman
2023-03-09 14:48 ` Arnd Bergmann
2023-03-09 17:37 ` Oliver Neukum
2023-03-09 17:30 ` Oliver Neukum [this message]
2023-03-10 5:01 ` Ye, Xiang
2023-03-10 7:11 ` Greg Kroah-Hartman
2023-03-10 7:39 ` Ye, Xiang
2023-03-10 7:53 ` Greg Kroah-Hartman
2023-03-10 8:59 ` Ye, Xiang
2023-03-11 12:13 ` Krzysztof Kozlowski
2023-03-12 15:40 ` Ye, Xiang
2023-03-09 7:10 ` [PATCH v4 3/5] i2c: Add support for Intel LJCA USB I2C driver Ye Xiang
2023-03-09 7:10 ` [PATCH v4 4/5] spi: Add support for Intel LJCA USB SPI driver Ye Xiang
2023-03-09 7:11 ` [PATCH v4 5/5] Documentation: Add ABI doc for attributes of LJCA device Ye Xiang
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