linux-kernel - Re: [PATCH v4 2/5] gpio: Add support for Intel LJCA USB GPIO driver

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Date:   Thu, 9 Mar 2023 18:37:30 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Oliver Neukum <oneukum@...e.com>, Ye Xiang <xiang.ye@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Lee Jones <lee@...nel.org>, Wolfram Sang <wsa@...nel.org>,
        Tyrone Ting <kfting@...oton.com>,
        Mark Brown <broonie@...nel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>, linux-usb@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        srinivas.pandruvada@...el.com, heikki.krogerus@...ux.intel.com,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        zhifeng.wang@...el.com, wentong.wu@...el.com, lixu.zhang@...el.com
Subject: Re: [PATCH v4 2/5] gpio: Add support for Intel LJCA USB GPIO driver



On 09.03.23 15:48, Arnd Bergmann wrote:
> On Thu, Mar 9, 2023, at 15:18, Linus Walleij wrote:
>> On Thu, Mar 9, 2023 at 2:53 PM Andy Shevchenko
>> <andriy.shevchenko@...ux.intel.com> wrote:
>>
>> Yups. And I think the solution looks something like this:
>>
>> u8 obuf[LJCA_GPIO_BUF_SIZE] __aligned(8);
>> u8 ibuf[LJCA_GPIO_BUF_SIZE] __aligned(8);
>>
>> __aligned(4) if it's 32bit DMA I guess? 8 always works that's
>> why we use it all over the IIO subsystem.
> 
> I think it must be __aligned(ARCH_DMA_MINALIGN), to account
> for architectures with non-coherent DMA.

In theory, yes, you can do that.
Is that a better solution than using what kmalloc() is
designed to provide. I don't think so.

	Regards
		Oliver