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

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Message-ID: <ZArYCD0r6n0sJ7LI@kroah.com>
Date:   Fri, 10 Mar 2023 08:11:04 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Ye, Xiang" <xiang.ye@...el.com>
Cc:     Oliver Neukum <oneukum@...e.com>, Arnd Bergmann <arnd@...db.de>,
        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>,
        Linus Walleij <linus.walleij@...aro.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, linux-gpio@...r.kernel.org,
        srinivas.pandruvada@...el.com, heikki.krogerus@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, 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 Fri, Mar 10, 2023 at 01:01:11PM +0800, Ye, Xiang wrote:
> On Thu, Mar 09, 2023 at 02:40:10PM +0100, Oliver Neukum wrote:
> > 
> > 
> > On 09.03.23 08:10, Ye Xiang wrote:
> > 
> > > +#define LJCA_GPIO_BUF_SIZE 60
> > > +struct ljca_gpio_dev {
> > > +	struct platform_device *pdev;
> > > +	struct gpio_chip gc;
> > > +	struct ljca_gpio_info *gpio_info;
> > > +	DECLARE_BITMAP(unmasked_irqs, LJCA_MAX_GPIO_NUM);
> > > +	DECLARE_BITMAP(enabled_irqs, LJCA_MAX_GPIO_NUM);
> > > +	DECLARE_BITMAP(reenable_irqs, LJCA_MAX_GPIO_NUM);
> > > +	u8 *connect_mode;
> > > +	/* mutex to protect irq bus */
> > > +	struct mutex irq_lock;
> > > +	struct work_struct work;
> > > +	/* lock to protect package transfer to Hardware */
> > > +	struct mutex trans_lock;
> > > +
> > > +	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.
> But obuf and ibuf does not used to do DMA transfer here.
> It is actually copied from or to ljca buffer to do URB transfer.

urb transfers _ARE_ DMA transfers.

> Should it still need to follow the DMA coherency rules?

Yes, all buffers for USB urbs are required to follow those rules.

thanks,

greg k-h