linux-kernel - Re: [PATCH v3 15/24] drm/i2c: tda998x: use irq for connection status and EDID read

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Message-ID: <20140124174752.GF15937@n2100.arm.linux.org.uk>
Date:	Fri, 24 Jan 2014 17:47:52 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Jean-Francois Moine <moinejf@...e.fr>,
	dri-devel@...ts.freedesktop.org, Dave Airlie <airlied@...il.com>,
	Rob Clark <robdclark@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 15/24] drm/i2c: tda998x: use irq for connection
	status and EDID read

On Fri, Jan 24, 2014 at 06:29:12PM +0100, Sebastian Hesselbarth wrote:
> On 01/22/14 23:27, Russell King - ARM Linux wrote:
>> On Sun, Jan 19, 2014 at 07:58:43PM +0100, Jean-Francois Moine wrote:
>>> This patch adds the optional treatment of the tda998x IRQ.
>>>
>>> The interrupt function is used to know the display connection status
>>> without polling and to speedup reading the EDID.
>>>
>>> The interrupt number may be defined either in the DT or at encoder set
>>> config time for non-DT boards.
>>>
>>> Signed-off-by: Jean-Francois Moine <moinejf@...e.fr>
>>> ---
> [...]
>>> @@ -720,6 +787,10 @@ tda998x_encoder_set_config(struct drm_encoder *encoder, void *params)
>>>   		priv->audio_port = p->audio_cfg;
>>>   		priv->audio_format = p->audio_format;
>>>   	}
>>> +
>>> +	priv->irq = p->irq;
>>> +	if (p->irq)
>>> +		tda_irq_init(priv);
>>
>> If we're going to do it this way, this should probably release the IRQ if
>> there was one before re-claiming it, just in case this function gets called
>> more than once by some driver using it.
>>
>> The alternative is, as I said before, to use the infrastructure which is
>> already there, namely setting the interrupt via struct i2c_client's
>> irq member.  Yes, that doesn't satisfy Sebastian's comment about using
>> a GPIO, but there's no sign of GPIO usage in here at the moment anyway.
>> So we might as well use what's already provided.
>
> Russell,
>
> I am fine with using an irq instead of gpio here. I remember you telling
> me on a similar patch, that from the gpio you can derive the irq but
> not the other way round. Anyway, I also remember reading discussions
> about DT gpios vs interrupts, and IIRC the outcome was that passing
> interrupts is fine, too.

Sebastian,

You can derive the irq from a gpio (using gpio_to_irq()), but you can't
derive a gpio from an irq.

It's annoying that i2c_client and the i2c board data do not allow a GPIO
to be specified, but only an IRQ, but that's a separate problem which when
solved will also get solved here.  So, I'm not too worried about the
"should this be an IRQ or should it be a GPIO" question here.

For us on ARM, it's less of a problem because we can just deal with GPIOs
or IRQs at the DT level, and so we don't care what's in i2c_client.

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