Hi Arnd,
On Wed, 23 Nov 2016 11:15:32 +0100 Arnd Bergmann wrote:
> On Wednesday, November 23, 2016 5:53:41 PM CET Jisheng Zhang wrote:
> > 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.
>
> Right, this sounds like the most straightforward choice.
>
> > 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,
sorry, this line should be:
u32 phys_addr, void *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.
>
> Wait, since you compute an index 'i' here, can't you just store 'i'
> directly in the descriptor instead of the pointer?
>
we need to store the pointer, it's to store the buffer allocated by
mvneta_frag_alloc()
Thanks,
Jisheng
