linux-kernel - Re: [PATCH v3 6/7] iio: pressure: bmp280: Add data ready trigger support

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Message-ID: <20240828181333.GA80267@vamoiridPC>
Date: Wed, 28 Aug 2024 20:13:33 +0200
From: Vasileios Amoiridis <vassilisamir@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Vasileios Amoiridis <vassilisamir@...il.com>, jic23@...nel.org,
	lars@...afoo.de, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, ang.iglesiasg@...il.com,
	linus.walleij@...aro.org, biju.das.jz@...renesas.com,
	javier.carrasco.cruz@...il.com, semen.protsenko@...aro.org,
	579lpy@...il.com, ak@...klinger.de, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/7] iio: pressure: bmp280: Add data ready trigger
 support

On Wed, Aug 28, 2024 at 05:17:40PM +0300, Andy Shevchenko wrote:
> On Wed, Aug 28, 2024 at 04:01:19PM +0200, Vasileios Amoiridis wrote:
> > On Mon, Aug 26, 2024 at 01:23:56PM +0300, Andy Shevchenko wrote:
> > > On Sat, Aug 24, 2024 at 02:02:22PM +0200, Vasileios Amoiridis wrote:
> > > > On Fri, Aug 23, 2024 at 11:06:28PM +0300, Andy Shevchenko wrote:
> > > > > On Fri, Aug 23, 2024 at 08:17:13PM +0200, Vasileios Amoiridis wrote:
> 
> ...
> 
> > > > > > +	irq = fwnode_irq_get(fwnode, 0);
> > > > > > +	if (!irq)
> > > > > 
> > > > > Are you sure this is correct check?
> > > > > 
> > > > Well, I think yes, because the function return either the Linux IRQ number
> > > > on success or a negative errno on failure.
> > > 
> > > Where is 0 mentioned in this?
> > > 
> > > > https://elixir.bootlin.com/linux/v6.10.6/source/drivers/base/property.c#L987
> > > > 
> > > > > > +		return dev_err_probe(data->dev, -ENODEV,
> > > > > 
> > > > > Shadowed error code.
> > > > 
> > > > I am not sure I understand what you mean here. You mean that there is no
> > > > chance that the first one will pass and this one will fail?
> > > 
> > > -ENODEV is not what fwnode_irq_get() returns on error.
> > > 
> > > > > > +				     "No interrupt found.\n");
> 
> ...
> 
> > > > > > +	desc = irq_get_irq_data(irq);
> > > > > > +	if (!desc)
> > > > > > +		return -EINVAL;
> > > > > 
> > > > > When may this fail?
> > > > 
> > > > I think that this will fail when Linux were not able to actually
> > > > register that interrupt.
> > > 
> > > Wouldn't fwnode_irq_get() fail already?
> > 
> > By looking at it again, I didn't reply correct here. This function
> > internally calls the irq_to_desc() which basically returns the
> > irq desctiptor for this irq. This function can return NULL in
> > case the interrupt is not found in the maple tree (CONFIG_SPARSE_IRQ)
> > or in case the interrupt number is bigger than the NR_IRQs which
> > the irq controller can handle (!CONFIG_SPARSE_IRQ).
> > 
> > So in my opinion, it makes sense to keep this check.
> 
> So, you mean that if fwnode_irq_get() succeeded there is a chance that returned
> Linux IRQ number is invalid?! If it's so, it's something new to me. I would like
> to see the details, please!
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

Hi Andy,

I did some more digging, and from my understanding, fwnode_irq_get()
directly returns the Linux IRQ which means that there should already
exist the irq_desc structure that is returned by the irq_to_desc().

So as you already said, I cannot see how this function can fail, if
the fwnode_irq_get() has succeeded. Thanks for asking the right
questions, I am getting to know things better.

Cheers,
Vasilis