linux-kernel - Re: [PATCH v12 net-next 1/9] mfd: ocelot: add helper to get regmap from a resource

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Message-ID: <20220701203453.GB3327062@euler>
Date:   Fri, 1 Jul 2022 13:34:53 -0700
From:   Colin Foster <colin.foster@...advantage.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Terry Bowman <terry.bowman@....com>,
        katie.morris@...advantage.com
Subject: Re: [PATCH v12 net-next 1/9] mfd: ocelot: add helper to get regmap
 from a resource

On Fri, Jul 01, 2022 at 10:23:36PM +0200, Andy Shevchenko wrote:
> On Fri, Jul 1, 2022 at 9:26 PM Colin Foster
> <colin.foster@...advantage.com> wrote:
> >
> > Several ocelot-related modules are designed for MMIO / regmaps. As such,
> > they often use a combination of devm_platform_get_and_ioremap_resource and
> > devm_regmap_init_mmio.
> >
> > Operating in an MFD might be different, in that it could be memory mapped,
> > or it could be SPI, I2C... In these cases a fallback to use IORESOURCE_REG
> > instead of IORESOURCE_MEM becomes necessary.
> >
> > When this happens, there's redundant logic that needs to be implemented in
> > every driver. In order to avoid this redundancy, utilize a single function
> > that, if the MFD scenario is enabled, will perform this fallback logic.
> 
> ...
> 
> > +       res = platform_get_resource(pdev, IORESOURCE_MEM, index);
> > +       if (res) {
> > +               regs = devm_ioremap_resource(dev, res);
> > +               if (IS_ERR(regs))
> > +                       return ERR_CAST(regs);
> 
> Why can't it be devm_platform_get_and_ioremap_resource() here?

It can... but it invokes prints of "invalid resource" during
initialization.

Here it was implied that I should break the function call out:
https://patchwork.kernel.org/project/netdevbpf/patch/20220628081709.829811-2-colin.foster@in-advantage.com/#24917551

> 
>   regs = devm_platform_get_and_ioremap_resource();
>   if (res) {
>     if (IS_ERR(regs))
>       return ERR_CAST();
>    return ...
>   }
> 
> > +               return devm_regmap_init_mmio(dev, regs, config);
> > +       }
> 
> ...
> 
> > +       return (map) ? map : ERR_PTR(-ENOENT);
> 
> Too many parentheses.
> 
> Also you may use short form of ternary operator:
> 
>        return map ?: ERR_PTR(-ENOENT);

Agreed, and I didn't know about that operator. When Vladimir suggested
it I thought it was a typo. I should've known better.

> 
> -- 
> With Best Regards,
> Andy Shevchenko