Message-ID: <f2276121-2e58-d6be-f253-8c639855da98@suse.com>
Date:   Thu, 9 Mar 2023 18:37:30 +0100
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Subject: Re: [PATCH v4 2/5] gpio: Add support for Intel LJCA USB GPIO driver
Content-Language: en-US
To:     Arnd Bergmann <arnd@arndb.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Oliver Neukum <oneukum@suse.com>, Ye Xiang <xiang.ye@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        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>,
        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,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        srinivas.pandruvada@intel.com, heikki.krogerus@linux.intel.com,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        zhifeng.wang@intel.com, wentong.wu@intel.com, lixu.zhang@intel.com
References: <20230309071100.2856899-1-xiang.ye@intel.com>
 <20230309071100.2856899-3-xiang.ye@intel.com>
 <2865f3d0-428b-0df1-fc50-f6af3cb9dac3@suse.com>
 <ZAnku01goVDCuNM+@smile.fi.intel.com>
 <CACRpkdYQfT=JXvmjKR_9O74H2dmwx1EF4QjCHM6fKAetpbrMOg@mail.gmail.com>
 <d307b36e-4901-458d-a366-eaf478a77412@app.fastmail.com>
From:   Oliver Neukum <oneukum@suse.com>
In-Reply-To: <d307b36e-4901-458d-a366-eaf478a77412@app.fastmail.com>
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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@linux.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