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SubjectRe: [PATCH net-next] net: ethernet: ti: cpdma: rate is not changed - correct case
On Thu, Dec 07, 2017 at 02:50:24PM -0500, David Miller wrote:
> From: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
> Date: Thu, 7 Dec 2017 21:48:56 +0200
>
> > On Wed, Dec 06, 2017 at 04:35:45PM -0500, David Miller wrote:
> >> From: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
> >> Date: Wed, 6 Dec 2017 16:41:18 +0200
> >>
> >> > If rate is the same as set it's correct case.
> >> >
> >> > Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
> >> > ---
> >> > Based on net-next/master
> >> >
> >> > drivers/net/ethernet/ti/davinci_cpdma.c | 2 +-
> >> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >> >
> >> > diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
> >> > index e4d6edf..dbe9167 100644
> >> > --- a/drivers/net/ethernet/ti/davinci_cpdma.c
> >> > +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
> >> > @@ -841,7 +841,7 @@ int cpdma_chan_set_rate(struct cpdma_chan *ch, u32 rate)
> >> > return -EINVAL;
> >> >
> >> > if (ch->rate == rate)
> >> > - return rate;
> >> > + return 0;
> >>
> >> Looking at the one and only caller of this function, cpsw_ndo_set_tx_maxrate, it
> >> makes sure this can never, ever, happen.
> > In current circumstances yes, it will never happen.
> > But I caught it while adding related code and better return 0 if upper caller
> > doesn't have such check. Suppose that cpdma module is responsible for itself
> > and if it's critical I can send this patch along with whole related series.
>
> You have to decide one way or the other, who is responsible.
>
> I think checking higher up is better because it's cheaper at that point to
> look at the per-netdev queue rate setting before moving down deeper into the
> driver specific data-structures.

No objection, but upper caller not always knows current rate and for doing like
this it needs read it first, and this is also some redundancy.

--
Regards,
Ivan Khoronzhuk

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