linux-kernel - Re: [PATCH v2 1/2] mfd: mfd-core: Add mechanism for removal of a subset of children

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Message-ID: <20200616133039.GU71940@ediswmail.ad.cirrus.com>
Date:   Tue, 16 Jun 2020 13:30:39 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Lee Jones <lee.jones@...aro.org>
CC:     <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>
Subject: Re: [PATCH v2 1/2] mfd: mfd-core: Add mechanism for removal of a
 subset of children

On Tue, Jun 16, 2020 at 02:22:59PM +0100, Lee Jones wrote:
> On Tue, 16 Jun 2020, Charles Keepax wrote:
> > On Tue, Jun 16, 2020 at 10:15:45AM +0100, Lee Jones wrote:
> > > On Tue, 16 Jun 2020, Charles Keepax wrote:
> > > > On Tue, Jun 16, 2020 at 08:58:34AM +0100, Lee Jones wrote:
> > > > > On Mon, 15 Jun 2020, Charles Keepax wrote:
> > > > Does this match how you would expect this to be used?
> > > 
> > > No, not at all.
> > > 
> > > > I do have some concerns. The code can't use mfd_get_cell since it
> > > > returns a const pointer, although the pointer in platform_device
> > > > isn't const so we access that directly, could update mfd_get_cell? We
> > > > also don't have access to mfd_dev_type outside of the mfd core so
> > > > its hard to check we are actually setting the mfd_cell of actual
> > > > MFD children, I guess just checking for mfd_cell being not NULL is
> > > > good enough?
> > > 
> > > Hmmm... looks like I missed the fact that you needed additional
> > > processing between the removal of each batch of devices.  My
> > > implementation simply handles the order in which devices are removed
> > > (a bit like initcall()s).
> > > 
> > > How about the inclusion of mfd_remove_devices_late(), whereby
> > > mfd_remove_devices() will refuse to remove devices tagged with
> > > MFD_DEP_LEVEL_HIGH.
> > > 
> > 
> > Yeah this should work fine for my use-case.
> > 
> > > Not sure why, but I really dislike the idea of device removal by
> > > arbitrary value/tag, as I see it spawning all sorts of weird and
> > > wonderful implications/hacks/abuse.
> > > 
> > 
> > Its definitely a spectrum with flexibility covering more
> > use-cases but also definitely opening things up to more abuse. If
> > you are more comfortable with this approach that is fine with me.
> > 
> > Would you like me to have a crack at coding it up this way? Or
> > did you want to do a patch?
> 
> Either/or.  I don't want to steal your thunder, but I'm happy to draft
> if you are.
> 

Been having a poke this afternoon as I had some spare time, so
will wing that up and you can take over if I am too far off the
mark :-)

Thanks,
Charles