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Date:   Mon, 7 Dec 2020 15:13:11 +0100
From:   Krzysztof Kozlowski <krzk@kernel.org>
To:     Bongsu Jeon <bongsu.jeon2@gmail.com>
Cc:     linux-nfc@lists.01.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Bongsu Jeon <bongsu.jeon@samsung.com>
Subject: Re: [PATCH net-next] nfc: s3fwrn5: Change irqflags
Message-ID: <20201207141311.GB34599@kozik-lap>
References: <20201207113827.2902-1-bongsu.jeon@samsung.com>
 <20201207115147.GA26206@kozik-lap>
 <CACwDmQDHXwqzmUE_jEmPcJnCcPrzn=7qT=4rp1MF3s30OM7uTQ@mail.gmail.com>
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On Mon, Dec 07, 2020 at 10:39:01PM +0900, Bongsu Jeon wrote:
> On Mon, Dec 7, 2020 at 8:51 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> >
> > On Mon, Dec 07, 2020 at 08:38:27PM +0900, Bongsu Jeon wrote:
> > > From: Bongsu Jeon <bongsu.jeon@samsung.com>
> > >
> > > change irqflags from IRQF_TRIGGER_HIGH to IRQF_TRIGGER_RISING for stable
> > > Samsung's nfc interrupt handling.
> >
> > 1. Describe in commit title/subject the change. Just a word "change irqflags" is
> >    not enough.
> >
> Ok. I'll update it.
> 
> > 2. Describe in commit message what you are trying to fix. Before was not
> >    stable? The "for stable interrupt handling" is a little bit vauge.
> >
> Usually, Samsung's NFC Firmware sends an i2c frame as below.
> 
> 1. NFC Firmware sets the gpio(interrupt pin) high when there is an i2c
> frame to send.
> 2. If the CPU's I2C master has received the i2c frame, NFC F/W sets
> the gpio low.
> 
> NFC driver's i2c interrupt handler would be called in the abnormal case
> as the NFC F/W task of number 2 is delayed because of other high
> priority tasks.
> In that case, NFC driver will try to receive the i2c frame but there
> isn't any i2c frame
> to send in NFC. It would cause an I2C communication problem.
> This case would hardly happen.
> But, I changed the interrupt as a defense code.
> If Driver uses the TRIGGER_RISING not LEVEL trigger, there would be no problem
> even if the NFC F/W task is delayed.

All this should be explained in commit message, not in the email.

> 
> > 3. This is contradictory to the bindings and current DTS. I think the
> >    driver should not force the specific trigger type because I could
> >    imagine some configuration that the actual interrupt to the CPU is
> >    routed differently.
> >
> >    Instead, how about removing the trigger flags here and fixing the DTS
> >    and bindings example?
> >
> 
> As I mentioned before,
> I changed this code because of Samsung NFC's I2C Communication way.
> So, I think that it is okay for the nfc driver to force the specific
> trigger type( EDGE_RISING).
> 
> What do you think about it?

Some different chip or some different hardware implementation could have
the signal inverted, e.g. edge falling, not rising. This is rather
a theoretical scenario but still such change makes the code more
generic, configurable with DTS. Therefore trigger mode should be
configured via DTS, not enforced by the driver.

Best regards,
Krzysztof