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SubjectRe: [PATCH v3 05/16] ipmi: kcs bmc: Turn the driver data-str uctures inside-out

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 <>
> > Reviewed-by: Zev Weiss <>
> > ---
> > 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

The serio subsystem does have the 'drvctl' sysfs knob that allows
userspace to dictate which serio chardev interface they want to connect
to a serio device driver. Maybe that's preferred over my "connect them
all" strategy?


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