[PATCH v4] Network driver for the Armada 370 and Armada XP ARM Marvell SoCs
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Tue Nov 13 06:34:19 EST 2012
François,
Thanks for your detailed review. I have a few comments/questions below
on specific topics.
On Sat, 3 Nov 2012 12:53:21 +0100, Francois Romieu wrote:
> > + if (rxq->descs == NULL) {
> > + netdev_err(pp->dev,
> > + "rxQ=%d: Can't allocate %d bytes for %d RX descr\n",
> > + rxq->id, rxq->size * MVNETA_DESC_ALIGNED_SIZE,
> > + rxq->size);
> > + return -ENOMEM;
> > + }
> > +
> > + BUG_ON(rxq->descs !=
> > + PTR_ALIGN(rxq->descs, MVNETA_CPU_D_CACHE_LINE_SIZE));
>
> There is no reason to crash.
Well, there is a reason: the hardware will not work properly if
rxq->descs is not aligned on a MVNETA_CPU_D_CACHE_LINE_SIZE boundary.
So one solution is to over-allocated to guarantee the alignment, but
since practically speaking MVNETA_CPU_D_CACHE_LINE_SIZE=32 and
dma_alloc_coherent() returns things that seem at least 32 bytes
aligned, it sounded overkill to include more code to fix a problem that
doesn't exist. This BUG_ON() is here solely for the purpose of noisily
letting the user know if this implicit assumption on the alignment of
dma_alloc_coherent() allocated buffer changes in the future. I can turn
this into an error if you prefer:
if (rxq->descs != PTR_ALIGN(rxq->descs, MVNETA_CPU_D_CACHE_LINE_SIZE)) {
netdev_err(pp->dev, "improper buffer alignement assumption, driver needs fixing\n");
dma_free_coherent(...);
return -EINVAL;
}
> (...]
> > +static int mvneta_txq_init(struct mvneta_port *pp,
> > + struct mvneta_tx_queue *txq)
> > +{
> > + txq->size = pp->tx_ring_size;
> > +
> > + /* Allocate memory for TX descriptors */
> > + txq->descs = dma_alloc_coherent(pp->dev->dev.parent,
> > + txq->size * MVNETA_DESC_ALIGNED_SIZE,
> > + &txq->descs_phys,
> > + DMA_BIDIRECTIONAL);
>
> &txq->descs_phys, DMA_BIDIRECTIONAL);
Aaah, thanks for pointing this one! It should have been GFP_KERNEL, not
DMA_BIDIRECTIONAL here.
> > + if (txq->descs == NULL) {
> > + netdev_err(pp->dev,
> > + "txQ=%d: Can't allocate %d bytes for %d TX descr\n",
> > + txq->id, txq->size * MVNETA_DESC_ALIGNED_SIZE,
> > + txq->size);
> > + return -ENOMEM;
> > + }
> > +
> > + /* Make sure descriptor address is cache line size aligned */
> > + BUG_ON(txq->descs !=
> > + PTR_ALIGN(txq->descs, MVNETA_CPU_D_CACHE_LINE_SIZE));
>
> There is no reason to crash.
Same as above :-)
> [...]
> > +static int mvneta_setup_rxqs(struct mvneta_port *pp)
> > +{
> > + int queue;
> > +
> > + for (queue = 0; queue < rxq_number; queue++) {
> > + int err = mvneta_rxq_init(pp, &pp->rxqs[queue]);
> > + if (err) {
> > + netdev_err(pp->dev,
> > + "%s: can't create RxQ rxq=%d\n",
>
> netdev_err(pp->dev, "%s: can't create RxQ rxq=%d\n",
>
> > + __func__, queue);
> > + mvneta_cleanup_rxqs(pp);
> > + return -ENODEV;
>
> mvneta_rxq_init should return a proper error code and it should be
> propagated (option: break instead of return and mvneta_setup_rxqs scoped
> err variable)
Besides turning the "return -ENODEV;" into "return err;", I don't see
what is the other problem here? mvneta_rxq_init() properly returns
-ENOMEM where there is a memory allocation failure, and
mvneta_cleanup_rxqs() properly cleans up *all* initialized rxqs. Is
there something I'm missing?
Thanks again for your review!
Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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