On Tue, 22 Nov 2016 22:04:12 +0100 Arnd Bergmann wrote:
> On Tuesday, November 22, 2016 5:48:41 PM CET Gregory CLEMENT wrote:
> > +#ifdef CONFIG_64BIT
> > + void *data_tmp;
> > +
> > + /* In Neta HW only 32 bits data is supported, so in order to
> > + * obtain whole 64 bits address from RX descriptor, we store
> > + * the upper 32 bits when allocating buffer, and put it back
> > + * when using buffer cookie for accessing packet in memory.
> > + * Frags should be allocated from single 'memory' region,
> > + * hence common upper address half should be sufficient.
> > + */
> > + data_tmp = mvneta_frag_alloc(pp->frag_size);
> > + if (data_tmp) {
> > + pp->data_high = (u64)upper_32_bits((u64)data_tmp) << 32;
> > + mvneta_frag_free(pp->frag_size, data_tmp);
> > + }
> >
>
> How does this work when the region spans a n*4GB address boundary?
indeed. We also make use of this driver on 64bit platforms. We use
different solution to make the driver 64bit safe.
solA: make use of the reserved field in the mvneta_rx_desc, such
as reserved2 etc. Yes, the field is marked as "for future use, PnC", but
now it's not used at all. This is one possible solution however.
solB: allocate a shadow buf cookie during init, e.g
rxq->descs_bufcookie = kmalloc(rxq->size * sizeof(void*), GFP_KERNEL);
then modify mvneta_rx_desc_fill a bit to save the 64bit pointer in
the shadow buf cookie, e.g
static void mvneta_rx_desc_fill(struct mvneta_rx_desc *rx_desc,
u32 phys_addr, u32 cookie,
struct mvneta_rx_queue *rxq)
{
int i;
rx_desc->buf_cookie = cookie;
rx_desc->buf_phys_addr = phys_addr;
i = rx_desc - rxq->descs;
rxq->descs_bufcookie[i] = cookie;
}
then fetch the desc from the shadow buf cookie in all code path, such
as mvneta_rx() etc.
Both solutions should not have the problems pointed out by Arnd.
Thanks,
Jisheng
