Messages in this thread | | | Date | Wed, 1 Jul 2009 18:18:23 -0700 | Subject | Re: [PATCH 1/2 v2] dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller | From | Dan Williams <> |
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On Fri, Jun 26, 2009 at 3:42 AM, Nicolas Ferre<nicolas.ferre@atmel.com> wrote: > This AHB DMA Controller (aka HDMA or DMAC on AT91 systems) is availlable on > at91sam9rl chip. It will be used on other products in the future. > > This first release covers only the memory-to-memory tranfer type. This is the > only tranfer type supported by this chip. On other products, it will be used > also for peripheral DMA transfer (slave API support to come). > > I used dmatest client without problem in different configurations to test it. > > Full documentation for this controller can be found in the SAM9RL datasheet: > http://www.atmel.com/dyn/products/product_card.asp?part_id=4243 > > Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com> > --- [..]
A quick review comment:
> +/** > + * atc_desc_get - get a unsused descriptor from free_list > + * @atchan: channel we want a new descriptor for > + */ > +static struct at_desc *atc_desc_get(struct at_dma_chan *atchan) > +{ > + struct at_desc *desc, *_desc; > + struct at_desc *ret = NULL; > + unsigned int i = 0; > + LIST_HEAD(tmp_list); > + > + spin_lock_bh(&atchan->lock); > + list_for_each_entry_safe(desc, _desc, &atchan->free_list, desc_node) { > + i++; > + if (async_tx_test_ack(&desc->txd)) { > + list_del(&desc->desc_node); > + ret = desc; > + break; > + } > + dev_dbg(chan2dev(&atchan->chan_common), > + "desc %p not ACKed\n", desc); > + } > + spin_unlock_bh(&atchan->lock); > + dev_vdbg(chan2dev(&atchan->chan_common), > + "scanned %u descriptors on freelist\n", i); > + > + /* no more descriptor available in initial pool : create some more */ > + if (!ret) { > + for (i = 0; i < INIT_NR_DESCS_PER_CHANNEL; i++) { > + desc = atc_alloc_descriptor(&atchan->chan_common, > + GFP_KERNEL);
This cannot be GFP_KERNEL as ->prep_dma_memcpy may be called from an atomic context. Given that this should only be done in emergency situations this allocation should probably happen one descriptor at a time, if it must happen at all. My recommendation is that if you find that the driver runs out of descriptors on a regular basis increase INIT_NR_DESCS_PER_CHANNEL and only operate with the descriptors allocated from atc_alloc_chan_resources(). As it stands this allows the descriptor list to grow without bounds.
Regards, Dan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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