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

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Date:   Thu, 5 Nov 2020 08:21:22 +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 08:46 +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?

> > > What happens when you don't cast to (uintptr_t) first?
> > 
> > On some systems at least the gcc will warn:
> > > warning: cast from pointer to integer of different size [-Wpointer-
> > to-int-cast]
> > 
> > I am pretty sure I did end up this double casting via trial and error
> > :)

It's not uncommon. :)

> > > > +static const struct of_device_id bd957x_of_match[] = {
> > > > +	{
> > > > +		.compatible = "rohm,bd9576",
> > > > +		.data = (void *)ROHM_CHIP_TYPE_BD9576,
> > > > +	},
> > > > +	{
> > > 
> > > You could put the 2 lines above on a single line.
> > 
> > Braces? I put braces on separate lines on purpose. Been doing this
> > after we had this discussion:
> > 
> > https://lore.kernel.org/lkml/20180705055226.GJ496@dell/
> > https://lore.kernel.org/lkml/20180706070559.GW496@dell/
> > 
> > ;)
> > 
> > I can change it if you wishfeel it is important - not a point I feel
> > like fighting over ;)
> > 
> 
> Ah. I guess you meant:
> static const struct of_device_id bd957x_of_match[] = {
>         { .compatible = "rohm,bd9576", .data = (void *)ROHM_CHIP_TYPE_BD9576, },
>         { .compatible = "rohm,bd9573", .data = (void *)ROHM_CHIP_TYPE_BD9573, },
>         {},
> }; 

This would be better, yes.

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