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

From: Alexander Aring <alex.aring@gmail.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Stefan Schmidt <stefan@datenfreihafen.org>,
	linux-wpan - ML <linux-wpan@vger.kernel.org>,
	"open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
	"linux-wireless@vger.kernel.org Wireless" 
	<linux-wireless@vger.kernel.org>,
	David Girault <david.girault@qorvo.com>,
	Romuald Despres <romuald.despres@qorvo.com>,
	Frederic Blain <frederic.blain@qorvo.com>,
	Nicolas Schodet <nico@ni.fr.eu.org>,
	Michael Hennerich <michael.hennerich@analog.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Varka Bhadram <varkabhadram@gmail.com>,
	Xue Liu <liuxuenetmail@gmail.com>, Alan Ott <alan@signal11.us>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v3 07/41] net: ieee802154: mcr20a: Fix lifs/sifs periods
Date: Tue, 18 Jan 2022 17:53:36 -0500	[thread overview]
Message-ID: <CAB_54W4Je4-jCMFkqATfj2c2+5By2PSWOqCUudt1+sgimFKhHw@mail.gmail.com> (raw)
In-Reply-To: <20220118192013.46c42f82@xps13>

Hi,

On Tue, 18 Jan 2022 at 13:20, Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Alexander,
>
> alex.aring@gmail.com wrote on Mon, 17 Jan 2022 17:52:10 -0500:
>
> > Hi,
> >
> > On Mon, 17 Jan 2022 at 06:54, Miquel Raynal <miquel.raynal@bootlin.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@bootlin.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