Messages in this thread | | | Date | Wed, 23 Nov 2016 17:53:41 +0800 | From | Jisheng Zhang <> | Subject | Re: [PATCH net-next 1/4] net: mvneta: Convert to be 64 bits compatible |
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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
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