linux-kernel - Re: [PATCH v4 2/4] mfd: Support ROHM BD9576MUF and BD9573MUF

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Date:   Thu, 5 Nov 2020 08:58:10 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
Cc:     "linux@...ck-us.net" <linux@...ck-us.net>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "mazziesaccount@...il.com" <mazziesaccount@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-power <linux-power@...rohmeurope.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH v4 2/4] mfd: Support ROHM BD9576MUF and BD9573MUF

On Thu, 05 Nov 2020, Vaittinen, Matti wrote:

> 
> On Thu, 2020-11-05 at 08:21 +0000, Lee Jones wrote:
> > On Thu, 05 Nov 2020, Vaittinen, Matti wrote:
> > 
> > > On Thu, 2020-11-05 at 08:46 +0200, Matti Vaittinen wrote:
> > > > Morning Lee,
> > > > 
> > > > Thanks for taking a look at this :) I see most of the comments
> > > > being
> > > > valid. There's two I would like to clarify though...
> > > > 
> > > > On Wed, 2020-11-04 at 15:51 +0000, Lee Jones wrote:
> > > > > On Wed, 28 Oct 2020, Matti Vaittinen wrote:
> > > > > 
> > > > > > Add core support for ROHM BD9576MUF and BD9573MUF PMICs which
> > > > > > are
> > > > > > mainly used to power the R-Car series processors.
> > > > > > 
> > > > > > Signed-off-by: Matti Vaittinen <
> > > > > > matti.vaittinen@...rohmeurope.com
> > > > > > ---
> > > > > > +	unsigned int chip_type;
> > > > > > +
> > > > > > +	chip_type = (unsigned int)(uintptr_t)
> > > > > > +		    of_device_get_match_data(&i2c->dev);
> > > > > 
> > > > > Not overly keen on this casting.
> > > > > 
> > > > > Why not just leave it as (uintptr_t)?
> > > > 
> > > > I didn't do so because on x86_64 the address width is probably 64
> > > > bits
> > > > whereas the unsigned int is likely to be 32 bits. So the
> > > > assignment
> > > > will crop half of the value. It does not really matter as values
> > > > are
> > > > small - but I would be surprized if no compilers/analyzers
> > > > emitted a
> > > > warning.
> > > > 
> > > > I must admit I am not 100% sure though. I sure can change this if
> > > > you
> > > > know it better?
> > 
> > What if you used 'long', which I believe changed with the
> > architecture's bus width in Linux?
> 
> I think this is exactly what uintptr_t was created for. To provide type
> which assures a pointer conversion to integer and back works.
> 
> I guess I can change the
> 
> unsigned int chip_type;
> 
> to uintptr_t and get away with single cast if it looks better to you.
> For me the double cast does not look that bad when it allows use of
> native int size variable - but in this case it's really just a matter
> of taste. Both should work fine.

I do see people casting to uintptr and placing the result into a long.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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