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Date:   Tue, 25 May 2021 09:42:34 +0930
From:   "Andrew Jeffery" <andrew@aj.id.au>
To:     "Corey Minyard" <minyard@acm.org>
Cc:     devicetree@vger.kernel.org, "Tomer Maimon" <tmaimon77@gmail.com>,
        linux-aspeed@lists.ozlabs.org,
        "Avi Fishman" <avifishman70@gmail.com>,
        "Patrick Venture" <venture@google.com>, openbmc@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, "Tali Perry" <tali.perry1@gmail.com>,
        "Rob Herring" <robh+dt@kernel.org>,
        "Arnd Bergmann" <arnd@arndb.de>,
        openipmi-developer@lists.sourceforge.net,
        "Zev Weiss" <zweiss@equinix.com>,
        "Chia-Wei, Wang" <chiawei_wang@aspeedtech.com>,
        linux-arm-kernel@lists.infradead.org,
        "Benjamin Fair" <benjaminfair@google.com>
Subject: =?UTF-8?Q?Re:_[Openipmi-developer]_[PATCH_v3_05/16]_ipmi:_kcs=5Fbmc:_Tur?=
 =?UTF-8?Q?n_the_driver_data-structures_inside-out?=
Content-Type: text/plain
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On Tue, 25 May 2021, at 01:11, Corey Minyard wrote:
> On Mon, May 24, 2021 at 10:23:36AM +0930, Andrew Jeffery wrote:
> > 
> > 
> > On Sat, 22 May 2021, at 02:44, Corey Minyard wrote:
> > > On Mon, May 10, 2021 at 03:12:02PM +0930, Andrew Jeffery wrote:
> > > > Make the KCS device drivers responsible for allocating their own memory.
> > > > 
> > > > Until now the private data for the device driver was allocated internal
> > > > to the private data for the chardev interface. This coupling required
> > > > the slightly awkward API of passing through the struct size for the
> > > > driver private data to the chardev constructor, and then retrieving a
> > > > pointer to the driver private data from the allocated chardev memory.
> > > > 
> > > > In addition to being awkward, the arrangement prevents the
> > > > implementation of alternative userspace interfaces as the device driver
> > > > private data is not independent.
> > > > 
> > > > Peel a layer off the onion and turn the data-structures inside out by
> > > > exploiting container_of() and embedding `struct kcs_device` in the
> > > > driver private data.
> > > 
> > > All in all a very nice cleanup.  A few nits inline.
> > > 
> > > > 
> > > > Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
> > > > Reviewed-by: Zev Weiss <zweiss@equinix.com>
> > > > ---
> > > >  drivers/char/ipmi/kcs_bmc.c           | 19 +++++++--
> > > >  drivers/char/ipmi/kcs_bmc.h           | 12 ++----
> > > >  drivers/char/ipmi/kcs_bmc_aspeed.c    | 56 +++++++++++++------------
> > > >  drivers/char/ipmi/kcs_bmc_cdev_ipmi.c | 60 ++++++++++++++++++---------
> > > >  drivers/char/ipmi/kcs_bmc_npcm7xx.c   | 37 ++++++++++-------
> > > >  5 files changed, 111 insertions(+), 73 deletions(-)
> > > > 
> > > > diff --git a/drivers/char/ipmi/kcs_bmc.c b/drivers/char/ipmi/kcs_bmc.c
> > > > index ef5c48ffe74a..83da681bf49e 100644
> > > > --- a/drivers/char/ipmi/kcs_bmc.c
> > > > +++ b/drivers/char/ipmi/kcs_bmc.c
> > > > @@ -44,12 +44,23 @@ int kcs_bmc_handle_event(struct kcs_bmc *kcs_bmc)
> > > >  }
> > > >  EXPORT_SYMBOL(kcs_bmc_handle_event);
> > > >  
> > > > -struct kcs_bmc *kcs_bmc_ipmi_alloc(struct device *dev, int sizeof_priv, u32 channel);
> > > > -struct kcs_bmc *kcs_bmc_alloc(struct device *dev, int sizeof_priv, u32 channel)
> > > > +int kcs_bmc_ipmi_add_device(struct kcs_bmc *kcs_bmc);
> > > 
> > > The above (and it's remove function) should be in an include file.
> > 
> > This is a short-term hack while I'm refactoring the code. It goes away 
> > in a later patch when we switch to using an ops struct.
> > 
> > I didn't move it to a header as it's an implementation detail at the 
> > end of the day. I see headers as describing a public interface, and in 
> > the bigger picture this function isn't part of the public API. But 
> > maybe it's too tricky by half. My approach here generated some 
> > discussion with Zev as well.
> > 
> > > 
> > > > +void kcs_bmc_add_device(struct kcs_bmc *kcs_bmc)
> > > 
> > > This should return an error so the probe can be failed and cleaned up
> > > and so confusing message don't get printed after this in one case.
> > 
> > Hmm. I did this because the end result of the series is that we can 
> > have multiple chardev interfaces in distinct modules exposing the one 
> > KCS device in the one kernel. If more than one of the chardev modules 
> > is configured in and one of them fails to initialise themselves with 
> > respect to the device driver I didn't think it was right to fail the 
> > probe of the device driver (and thus remove any chardev interfaces that 
> > did succeed to initialise against it).
> > 
> > But this does limit the usefulness of the device driver instance in the 
> > case that only one of the chardev interfaces is configured in and it 
> > fails to initialise.
> > 
> > So I think we need to decide on the direction before I adjust the 
> > interface here. The patches are architected around the idea of multiple 
> > chardevs being configured in to the kernel build and all are exposed at 
> > runtime.
> 
> Ok, I understand.  The host IPMI driver will attempt to start all
> interfaces, if none fail to come up it will return an error, but if any
> come up it will not return an error.  So it's a similar situation.

That sounds reasonable. I'll implement this strategy.

> 
> I stole that from something else, but I can't remember what.  I don't
> know what the best policy is, really, that was kind of a compromise and
> nobody has complained about it.
> 
> I will say that the success print in aspeed_kcs_probe() needs to not
> happen if there is a failure, though.

With the strategy you outlined above that's easy enough.

Thanks,

Andrew