Re: [PATCH v2 1/2] i2c/busses: Diolan U2C-12 USB/I2C adapter driver

[Guenter Roeck <guenter.roeck-IzeFyvvaP7pWk0Htik3J/w@public.gmane.org>]

On Wed, 2011-01-19 at 16:14 -0500, Ben Dooks wrote:
> On Wed, Jan 19, 2011 at 01:26:37PM -0800, Guenter Roeck wrote:
> > Signed-off-by: Guenter Roeck <guenter.roeck-IzeFyvvaP7pWk0Htik3J/w@public.gmane.org>
 [ ... ]

> > +/* Structure to hold all of our device specific stuff */
> > +struct i2c_diolan_u2c {
> > +	struct usb_device *usb_dev;	/* the usb device for this device */
> > +	struct usb_interface *interface;/* the interface for this device */
> > +	struct i2c_adapter adapter;	/* i2c related things */
> > +	int olen;			/* Output buffer length */
> > +	int ocount;			/* Number of enqueued messages */
> > +	u8 obuffer[DIOLAN_OUTBUF_LEN];	/* output buffer */
> > +	u8 ibuffer[DIOLAN_INBUF_LEN];	/* input buffer */
> 
> you should cache-line align the buffers to avoid any problems with
> dma-vs-cache, etc.
> 
There are several other drivers which don't cache-align the buffers used
with usb_bulk_msg(). Do those all have potential problems, or is this
only relevant for optimization ?

If it is just for optimization, I'd argue that the speed here is so slow
that it won't make much of a difference, if any, if the buffers were
aligned.

Thanks,
Guenter