linux-kernel - Re: [PATCH 571/606] serial: sc16is7xx: Convert to i2c's .probe

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Message-ID: <Y9O5cMnC+uKrPToz@kroah.com>
Date:   Fri, 27 Jan 2023 12:45:52 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
        Uwe Kleine-König <uwe@...ine-koenig.org>,
        linux-kernel@...r.kernel.org, Wolfram Sang <wsa@...nel.org>,
        Angel Iglesias <ang.iglesiasg@...il.com>,
        linux-i2c@...r.kernel.org, kernel@...gutronix.de,
        Grant Likely <grant.likely@...aro.org>,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 571/606] serial: sc16is7xx: Convert to i2c's .probe_new()

On Fri, Jan 27, 2023 at 11:10:25AM +0100, Uwe Kleine-König wrote:
> Hello,
> 
> On Wed, Nov 23, 2022 at 09:09:12AM +0100, Uwe Kleine-König wrote:
> > On Wed, Nov 23, 2022 at 07:36:52AM +0100, Jiri Slaby wrote:
> > > On 21. 11. 22, 8:07, Uwe Kleine-König wrote:
> > > > On Mon, Nov 21, 2022 at 07:03:41AM +0100, Jiri Slaby wrote:
> > > > > On 18. 11. 22, 23:45, Uwe Kleine-König wrote:
> > > > > > From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > > > > 
> > > > > > .probe_new() doesn't get the i2c_device_id * parameter, so determine
> > > > > > that explicitly in the probe function.
> > > > > 
> > > > > I wonder why -- is this a new approach to probe functions? Or is only i2c
> > > > > affected? And why? Could you point to the commit introducing and describing
> > > > > the change in the i2c core?
> > > > 
> > > > I didn't sent the cover letter to all recipents of the individual
> > > > patches, so flow of information is a bit rough. Sorry about that.
> > > > 
> > > > You can find it at
> > > > https://lore.kernel.org/lkml/20221118224540.619276-1-uwe@kleine-koenig.org/,
> > > > it should answer your question.
> > > 
> > > Yes, I looked up that beforehand, but was no more clever after reading it.
> > > 
> > > > The short version is: The i2c framework does a more or less expensive
> > > > lookup for each call to .probe() to provide the id parameter. A relevant
> > > > part of the drivers however doesn't use this parameter, so the idea is
> > > > to let the drivers who actually need it, determine it themselves.
> > > > 
> > > > Statistics for the current state of this series in my tree:
> > > > Among the 602 converted drivers, 404 don't make use of the parameter.
> > > 
> > > So doesn't it make sense to provide both probe with no id and "probe_id"
> > > then? 200 is quite a few (a third to be precise).
> > 
> > Having the probe callback with the id parameter is only temporary. As
> > soon as all drivers are converted, the variant with the id parameter
> > will go away.
> > 
> > > BTW is this a performance issue? I.e. does it slow down the boot?
> > 
> > I don't know the start motivation for Lee (who triggered the conversion
> > in b8a1a4cd5a98 ("i2c: Provide a temporary .probe_new() call-back
> > type")).
> > Looking at the git history, he created 1e98dcd77970 ("mfd: 88pm860x:
> > Move over to new I2C device .probe() call") converting a driver that
> > doesn't benefit immensely. The lookup is more expensive for drivers with
> > big .id_table, the converted driver has only one entry.
> > 
> > I think in the end is a mixture between:
> > 
> >  - A big part of the drivers doesn't benefit from the lookup.
> >  - For most other busses the probe function only gets a device parameter
> >    and no id (spi, platform, i3c). There are counter examples though:
> >    amba, usb. Didn't check further.
> 
> The discussion somehow ended here without a real result.
> 
> As of today's next master there are only 9 drivers left using .probe().
> So I'd like to stop this discussion and ask to apply the conversion for
> the sc16is7xx driver to be able to complete the conversion.
> 
> My plan is to drop the .probe callback as it is today after the next
> merge window. So I ask the serial maintainers to either take the patch
> under discussion for the next merge window or accept that the conversion
> is done together with the patch that drops .probe() that probably will
> go in via the i2c tree.

I don't see the patch anymore, so I have no objection for it going
through the i2c tree.

thanks,

greg k-h