linux-kernel - Re: [PATCH v2 2/2] watchdog: Add new arm_smc

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Date:   Tue, 21 Apr 2020 13:31:25 -0700
From:   Julius Werner <jwerner@...omium.org>
To:     Evan Benn <evanbenn@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Xingyu Chen <xingyu.chen@...ogic.com>,
        Julius Werner <jwerner@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Anson Huang <Anson.Huang@....com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Leonard Crestez <leonard.crestez@....com>,
        Li Yang <leoyang.li@....com>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Olof Johansson <olof@...om.net>, Rob Herring <robh@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Will Deacon <will@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        LINUX-WATCHDOG <linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] watchdog: Add new arm_smc_wdt watchdog driver

> +static int smcwd_call(unsigned long smc_func_id, enum smcwd_call call,
> +                     unsigned long arg, struct arm_smccc_res *res)

I think you should just take a struct watchdog_device* here and do the
drvdata unpacking inside the function.

> +static int smcwd_probe(struct platform_device *pdev)
> +{
> +       struct watchdog_device *wdd;
> +       int err;
> +       struct arm_smccc_res res;
> +       u32 *smc_func_id;
> +
> +       smc_func_id =
> +               devm_kzalloc(&pdev->dev, sizeof(*smc_func_id), GFP_KERNEL);
> +       if (!smc_func_id)
> +               return -ENOMEM;

nit: Could save the allocation by just casting the value itself to a
pointer? Or is that considered too hacky?

> +static const struct of_device_id smcwd_dt_ids[] = {
> +       { .compatible = "mediatek,mt8173-smc-wdt" },
> +       {}
> +};
> +MODULE_DEVICE_TABLE(of, smcwd_dt_ids);

So I'm a bit confused about this... I thought the plan was to either
use arm,smc-id and then there'll be no reason to put platform-specific
quirks into the driver, so we can just use a generic "arm,smc-wdt"
compatible string on all platforms; or we put individual compatible
strings for each platform and use them to hardcode platform-specific
differences (like the SMC ID) in the driver. But now you're kinda
doing both by making the driver code platform-independent but still
using a platform-specific compatible string, that doesn't seem to fit
together. (If the driver can be platform independent, I think it's
nicer to have a generic compatible string so that future platforms
which support the same interface don't have to land code changes in
order to just use the driver.)