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

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

On Thu, Mar 09, 2023 at 03:52:59PM +0200, 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:
> > 
> > > +#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.
> 
> 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.

As you said, the problem is alignment.