linux-kernel - Re: [PATCH] iio: adc: ti-ads7950: add GPIO support

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Date:   Mon, 11 Feb 2019 12:17:37 -0800
From:   Justin Chen <justinpopo6@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     David Lechner <david@...hnology.com>, linux-iio@...r.kernel.org,
        linux-gpio@...r.kernel.org,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        bgolaszewski@...libre.com,
        Linus Walleij <linus.walleij@...aro.org>, knaack.h@....de,
        lars@...afoo.de, Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: ti-ads7950: add GPIO support

On Mon, Feb 11, 2019 at 12:06 PM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Sat, 9 Feb 2019 12:56:11 -0600
> David Lechner <david@...hnology.com> wrote:
>
> > On 2/9/19 11:00 AM, Jonathan Cameron wrote:
> > > Nope.  This is a state lock used to protect against transitions between
> > > different modes of the IIO device (buffered vs polled), it
> > > isn't suitable for general use.
> > >
> > > The driver should be modified to handle that correctly.
> > > We have iio_claim_direct_mode etc that deal with the case
> > > where a device can't do certain operations whilst in buffered
> > > mode.  Note it can fail and should.
> > >
> > > Seems there are more drivers still doing this than I thought.
> > > If anyone is bored and wants to clean them out, that would be
> > > most appreciated!
> > >
> > > If you need locking to protect a local buffer or the device
> > > state, define a new lock to do it with clearly documented
> > > scope.
> >
> > Just as a reminder, there is a use case for this particular
> > chip that requires buffered mode and direct mode at the same
> > time.
> >
> > https://patchwork.kernel.org/patch/10539021/
> > https://patchwork.kernel.org/patch/10527757/
>
> Thanks, I had indeed forgotten that entirely.
> So it should have a local lock and not take mlock explicitly at all.
>
Thanks for all the feedback.
So If I am understanding this correctly. I should create a local lock
to synchronize three different type of transactions (buffered, direct,
gpio).
I do not want to use iio_claim_direct_mode because that doesn't allow
simultaneous use of buffered mode and direct mode, which is necessary
for this driver because of the above mentioned patch.

Justin
> Jonathan