Re: [PATCH v9 6/9] i3c: master: Add driver for Cadence IP

[Boris Brezillon]

On Thu, 25 Oct 2018 17:30:26 +0200
Arnd Bergmann <arnd@xxxxxxxx> wrote:

> On 10/24/18, Boris Brezillon <boris.brezillon@xxxxxxxxxxx> wrote:
> > Hi Arnd,
> >
> > On Mon, 22 Oct 2018 15:34:01 +0200
> > Boris Brezillon <boris.brezillon@xxxxxxxxxxx> wrote:
> >
> >  
> >> +
> >> +static void cdns_i3c_master_rd_from_rx_fifo(struct cdns_i3c_master
> >> *master,
> >> +					    u8 *bytes, int nbytes)
> >> +{
> >> +	readsl(master->regs + RX_FIFO, bytes, nbytes / 4);  
> >
> > Vitor reported a problem with readsl(): this function expects the 2nd
> > argument to be aligned on 32-bit, which is not guaranteed here. Unless
> > you see a better solution, I'll switch back to a loop doing:
> >
> > 	for (i = 0; i < nbytes; i += 4) {
> > 		u32 tmp = __raw_readl(...);
> > 		memcpy(bytes + i, &tmp,
> > 		       nbytes - i  > 4 ? 4 : nbytes - i);
> > 	}  
> 
> Could we maybe mandate that the buffer itself must be aligned here?
> What would be a reason why we see an unaligned target buffer?

Well, the buffers we pass to i3c_send_ccc_cmd() are not necessarily
aligned because they're not dynamically allocated (allocated on the
stack) and are not naturally aligned on 32-bits (either because they
are smaller than 32bits or because the struct is declared __packed).

I guess I could dynamically allocate the payload, but that requires
going over all users of i3c_send_ccc_cmd() to patch them.