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

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Date:   Mon, 11 Feb 2019 20:05:57 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     David Lechner <david@...hnology.com>
Cc:     justinpopo6@...il.com, linux-iio@...r.kernel.org,
        linux-gpio@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        f.fainelli@...il.com, bgolaszewski@...libre.com,
        linus.walleij@...aro.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: ti-ads7950: add GPIO support

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.

Jonathan