linux-kernel - Re: [PATCH v4 06/10] ARM: defconfig: Use the new FSL QSPI driver under the SPI framework

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Message-ID: <20181108093451.08dfe63e@bbrezillon>
Date:   Thu, 8 Nov 2018 09:34:51 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Schrempf Frieder <frieder.schrempf@...tron.De>
Cc:     Olof Johansson <olof@...om.net>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Brian Norris" <computersforpeace@...il.com>,
        Mark Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        Mark Brown <broonie@...nel.org>,
        "david.wolfe@....com" <david.wolfe@....com>,
        Fabio Estevam <fabio.estevam@....com>,
        "prabhakar.kushwaha@....com" <prabhakar.kushwaha@....com>,
        "yogeshnarayan.gaur@....com" <yogeshnarayan.gaur@....com>,
        "han.xu@....com" <han.xu@....com>, Shawn Guo <shawnguo@...nel.org>,
        "frieder.schrempf@...eet.de" <frieder.schrempf@...eet.de>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        "Sascha Hauer" <kernel@...gutronix.de>,
        "linux-imx@....com" <linux-imx@....com>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Eric Anholt <eric@...olt.net>, Stefan Agner <stefan@...er.ch>,
        Simon Horman <horms+renesas@...ge.net.au>,
        Tony Lindgren <tony@...mide.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Stefan Wahren <stefan.wahren@...e.com>,
        "yannick.fertre@...com" <yannick.fertre@...com>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 06/10] ARM: defconfig: Use the new FSL QSPI driver
 under the SPI framework

On Wed, 7 Nov 2018 16:36:13 +0000
Schrempf Frieder <frieder.schrempf@...tron.De> wrote:

> Hi Olof,
> 
> On 07.11.18 17:20, Olof Johansson wrote:
> > On Wed, Nov 7, 2018 at 6:44 AM Frieder Schrempf
> > <frieder.schrempf@...tron.de> wrote:  
> >>
> >> From: Frieder Schrempf <frieder.schrempf@...eet.de>
> >>
> >> The new driver at spi/spi-fsl-qspi.c replaces the old SPI NOR driver
> >> at mtd/fsl-quadspi.c. Switch to the new driver in the defconfigs.
> >>
> >> Signed-off-by: Frieder Schrempf <frieder.schrempf@...eet.de>  
> > 
> > Hi Frieder,
> > 
> > This patch is part of a series that I didn't see the rest of, but in
> > general we prefer to merge these through arm-soc even if the driver
> > goes in through another tree. The way we'd prefer to handle it is that
> > once the driver lands, we'll take the config option change to turn it
> > on. To avoid our branches to break until both sides have landed, it
> > might be a good idea to keep both drivers on for a short while (one
> > release).
> > 
> > So, I'm not going to ack this since we avoid taking defconfig changes
> > through driver trees (these two defconfigs tend to churn a lot and we
> > don't want to create merge conflicts where we don't have to), but
> > we'll be happy to pick it up when the time comes.  
> 
> Ok, thank you for explaining the common practice. I will drop the config 
> changes for the next version and send it separately when the time is ready.
> 
> Both the old driver and the new one use the same compatible strings for 
> probing. Wouldn't that cause problems if both drivers are enabled for a 
> while, or am I missing something?

Or maybe we should not introduce a new Kconfig option and just reuse
the old one. It probably requires re-ordering patches a bit (patch 1
should be moved after patch 5). Then you have 2 choices:

1/ merge patch 1 and 6 so that the new driver effectively replaces the
   old one but uses the same Kconfig option
2/ remove the ability to compile the old driver when the new one is
   introduced: remove the line from drivers/mtd/spi-nor Makefile and
   move the Kconfig entry from drivers/mtd/spi-nor/Kconfig to
   drivers/spi/Kconfig. And remove the old code in a separate patch

I'm fine either way, but option #2 will probably make the patch
introducing the new driver bigger and hurt readability.