netdev - Re: [PATCH v3 07/41] net: ieee802154: mcr20a: Fix lifs/sifs periods

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Message-ID: <CAB_54W4Je4-jCMFkqATfj2c2+5By2PSWOqCUudt1+sgimFKhHw@mail.gmail.com>
Date:   Tue, 18 Jan 2022 17:53:36 -0500
From:   Alexander Aring <alex.aring@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <linux-wpan@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org Wireless" 
        <linux-wireless@...r.kernel.org>,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Varka Bhadram <varkabhadram@...il.com>,
        Xue Liu <liuxuenetmail@...il.com>, Alan Ott <alan@...nal11.us>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 07/41] net: ieee802154: mcr20a: Fix lifs/sifs periods

Hi,

On Tue, 18 Jan 2022 at 13:20, Miquel Raynal <miquel.raynal@...tlin.com> wrote:
>
> Hi Alexander,
>
> alex.aring@...il.com wrote on Mon, 17 Jan 2022 17:52:10 -0500:
>
> > Hi,
> >
> > On Mon, 17 Jan 2022 at 06:54, Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> > >
> > > These periods are expressed in time units (microseconds) while 40 and 12
> > > are the number of symbol durations these periods will last. We need to
> > > multiply them both with phy->symbol_duration in order to get these
> > > values in microseconds.
> > >
> > > Fixes: 8c6ad9cc5157 ("ieee802154: Add NXP MCR20A IEEE 802.15.4 transceiver driver")
> > > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > > ---
> > >  drivers/net/ieee802154/mcr20a.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/ieee802154/mcr20a.c b/drivers/net/ieee802154/mcr20a.c
> > > index f0eb2d3b1c4e..e2c249aef430 100644
> > > --- a/drivers/net/ieee802154/mcr20a.c
> > > +++ b/drivers/net/ieee802154/mcr20a.c
> > > @@ -976,8 +976,8 @@ static void mcr20a_hw_setup(struct mcr20a_local *lp)
> > >         dev_dbg(printdev(lp), "%s\n", __func__);
> > >
> > >         phy->symbol_duration = 16;
> > > -       phy->lifs_period = 40;
> > > -       phy->sifs_period = 12;
> > > +       phy->lifs_period = 40 * phy->symbol_duration;
> > > +       phy->sifs_period = 12 * phy->symbol_duration;
> >
> > I thought we do that now in register_hw(). Why does this patch exist?
>
> The lifs and sifs period are wrong.
>
> Fixing this silently by generalizing the calculation is simply wrong. I
> feel we need to do this in order:
> 1- Fix the period because it is wrong.
> 2- Now that the period is set to a valid value and the core is able to
>    do the same operation and set the variables to an identical content,
>    we can drop these lines from the driver.
>
> #2 being a mechanical change, doing it without #1 means that something
> that appears harmless actually changes the behavior of the driver. We
> generally try to avoid that, no?

yes, maybe Stefan can get this patch then somehow to wpan and queue it
for stable.

Thanks for clarification.

- Alex