On Tue, 7 Jun 2011 14:41:35 +0100, Ben Dooks wrote: > On Tue, Jun 07, 2011 at 02:00:23PM +0100, Jonathan Cameron wrote: > > On 06/07/11 13:39, anish wrote: > > > From: anish kumar <[email protected]> > > > > > > replaced kmalloc with local variable as I2C(in this case) doesn't require > > > kmalloc memory it can do with stack memory. > > I've cc'd linux-i2c just to check I'm right about the whole i2c doesn't need > > dma safe buffers bit... > > No, it is down to the i2c driver, and from recollection dma from stack is > not recommended, due to things like cache line alignment. Please do not > do this.
To be clearer, it is down to the i2c BUS (adapter) driver, NOT the i2c device driver. So the patch is correct. Keep in mind that not all I2C/SMBus controllers care about DMA. In fact, most don't (at least in the set I am maintaining - might be different an embedded.) So calling kmalloc for every transfer in every I2C device driver "just in case" is very much counterproductive. And, if a controller does DMA and needs well-aligned, dynamically allocated buffer, its driver would hopefully allocate the buffer ONCE and keep it around, rather than reallocating it for every transfer. -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
