Hello,
On Tue, Jul 26, 2016 at 05:25:58PM +0300, Grygorii Strashko wrote:
> On 07/26/2016 03:02 PM, Uwe Kleine-König wrote:
> > Allocating and preparing a dma descriptor doesn't need to happen under
> > the channel's lock. So do this before taking the channel's lock. The only
> > down side is that the dma descriptor might be allocated even though the
> > channel is about to be stopped. This is unlikely though.
> >
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > ---
> > drivers/net/ethernet/ti/davinci_cpdma.c | 38 +++++++++++++++++----------------
> > 1 file changed, 20 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
> > index 5ffa04a306c6..ba3462707ae3 100644
> > --- a/drivers/net/ethernet/ti/davinci_cpdma.c
> > +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
> > @@ -542,24 +542,10 @@ int cpdma_chan_submit(struct cpdma_chan *chan, void *token, void *data,
> > u32 mode;
> > int ret = 0;
> >
> > - spin_lock_irqsave(&chan->lock, flags);
> > -
> > - if (chan->state == CPDMA_STATE_TEARDOWN) {
> > - ret = -EINVAL;
> > - goto unlock_ret;
> > - }
> > -
> > - if (chan->count >= chan->desc_num) {
> > - chan->stats.desc_alloc_fail++;
> > - ret = -ENOMEM;
> > - goto unlock_ret;
> > - }
>
> I'm not sure this is right thing to do. This check is expected to be strict
> and means "channel has exhausted the available descriptors, so further descs allocation does not allowed".
I developed this patch basing on a 4.4 kernel which doesn't have
742fb20fd4c7 ("net: ethernet: ti: cpdma: switch to use genalloc"). There
my patch is more obviously correct. As currently chan->count is
protected by chan->lock we must hold the lock for this check. If a
failing check means we must not call cpdma_desc_alloc in the first
place, that's bad.
But I'm not sure this is the case here. After all cpdma_desc_alloc
doesn't do anything relevant for the hardware, right?
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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