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SubjectRe: [PATCH net-next] net: ethernet: ti: cpdma: rate is not changed - correct case
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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.

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