linux-kernel - Re: [PATCH 2/3] soc: Add VIA/WonderMedia SoC identification driver

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Message-ID: <CABjd4YzQVQD1PCh3fUOzy_cwhd4j6q_N6zvb=kY4gFt-bn1Psg@mail.gmail.com>
Date: Fri, 25 Apr 2025 16:15:10 +0400
From: Alexey Charkov <alchark@...il.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/3] soc: Add VIA/WonderMedia SoC identification driver

On Fri, Apr 25, 2025 at 2:24 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On 23/04/2025 21:18, Alexey Charkov wrote:
> > Add a small SOC bus driver to parse the chip ID and revision made
> > available on VIA/WonderMedia SoCs via their system configuration
> > controller's SCC_ID register.
>
>
> ...
>
> > +#include <linux/io.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_platform.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/slab.h>
> > +#include <linux/sys_soc.h>
> > +
> > +static struct {
>
> I think const by convention is placed here - right after static. It
> should be equivalent, just convention.

Makes sense, thank you. Will adjust in v2.

> > +     const char *name;
> > +     const unsigned long id;
> > +} const chip_id_table[] = {
> > +     /* VIA */
> > +     { "VT8420", 0x3300 },
> > +     { "VT8430", 0x3357 },
> > +     { "VT8500", 0x3400 },
> > +
> > +     /* WonderMedia */
> > +     { "WM8425", 0x3429 },
> > +     { "WM8435", 0x3437 },
> > +     { "WM8440", 0x3451 },
> > +     { "WM8505", 0x3426 },
> > +     { "WM8650", 0x3465 },
> > +     { "WM8750", 0x3445 },
> > +     { "WM8850", 0x3481 },
> > +     { "WM8880", 0x3498 },
> > +};
> > +
> > +static const char *sccid_to_name(unsigned long sccid)
> > +{
> > +     unsigned long id = sccid >> 16;
> > +     unsigned int i;
> > +
> > +     for (i = 0 ; i < ARRAY_SIZE(chip_id_table) ; ++i) {
> > +             if (chip_id_table[i].id == id)
> > +                     return chip_id_table[i].name;
> > +     }
> > +
> > +     return "Unknown";
> > +}
> > +
> > +static const char *sccid_to_rev(unsigned long sccid)
> > +{
> > +     char letter, digit;
> > +
> > +     letter = (sccid >> 8) & 0xf;
> > +     letter = (letter - 1) + 'A';
> > +
> > +     digit = sccid & 0xff;
> > +     digit = (digit - 1) + '0';
> > +
> > +     return kasprintf(GFP_KERNEL, "%c%c", letter, digit);
> > +}
> > +
> > +static int __init wmt_socinfo_init(void)
> > +{
> > +     struct soc_device_attribute *attrs;
> > +     struct soc_device *soc_dev;
> > +     struct device_node *np;
> > +     void __iomem *reg;
> > +     unsigned long sccid;
> > +     const char *machine = NULL;
> > +
> > +     np = of_find_compatible_node(NULL, NULL, "via,scc-id");
> > +     if (!of_device_is_available(np)) {
> > +             of_node_put(np);
> > +             return -ENODEV;
> > +     }
> > +
> > +     reg = of_iomap(np, 0);
>
> of_node_put(np) here... although this will be dropped (see below)
>
>
> > +     if (!reg) {
> > +             of_node_put(np);
> > +             return -ENODEV;
> > +     }
> > +     sccid = readl(reg);
> > +     iounmap(reg);
> > +
> > +     attrs = kzalloc(sizeof(*attrs), GFP_KERNEL);
> > +     if (!attrs)
> > +             return -ENODEV;
> > +
> > +     /*
> > +      * Machine: VIA APC Rock
> > +      * Family: WM8850
> > +      * Revision: A2
> > +      * SoC ID: raw silicon revision id (0x34810103)
> > +      */
> > +
> > +     np = of_find_node_by_path("/");
> > +     of_property_read_string(np, "model", &machine);
> > +     if (machine)
> > +             attrs->machine = kstrdup(machine, GFP_KERNEL);
> > +     of_node_put(np);
> > +
> > +     attrs->family = sccid_to_name(sccid);
> > +     attrs->revision = sccid_to_rev(sccid);
> > +     attrs->soc_id = kasprintf(GFP_KERNEL, "%08lx", sccid);
> > +
> > +     soc_dev = soc_device_register(attrs);
> > +     if (IS_ERR(soc_dev)) {
> > +             kfree(attrs->machine);
> > +             kfree(attrs->soc_id);
> > +             kfree(attrs->revision);
> > +             kfree(attrs);
> > +             return PTR_ERR(soc_dev);
> > +     }
> > +
> > +     pr_info("VIA/WonderMedia %s rev %s (%s)\n",
> > +                     attrs->family,
> > +                     attrs->revision,
> > +                     attrs->soc_id);
> > +
> > +     return 0;
> > +}
> > +early_initcall(wmt_socinfo_init);
>
> No, this does not scale. This is supposed to be module_platform_driver
> instead of manually re-ordering code. Then all your memory allocations
> become devm, printks become dev_xxx and you can simplify it.

Fair enough. Will convert into a platform driver and use managed
functions. Thanks for pointing this out!

Best regards,
Alexey