Re: [PATCH 1/3] watchdog: qcom: add support for KPSS WDT

Josh Cartwright
2014-09-19T03:30:31Z

On Thu, Sep 18, 2014 at 07:41:17PM -0700, Guenter Roeck wrote:
> On 09/18/2014 03:26 PM, Josh Cartwright wrote:
> >Add a driver for the watchdog timer block found in the Krait Processor
> >Subsystem (KPSS) on the MSM8960, APQ8064, and IPQ8064.
> >
> >Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
>
> Hi Josh,
>
> comments inline.

Thanks for taking a look!

[..]
> >+static int qcom_watchdog_probe(struct platform_device *pdev)
> >+{
> >+ struct qcom_wdt *wdt;
> >+ struct resource *res;
> >+ u32 tmp;
> >+ int ret;
> >+
> >+ wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
> >+ if (!wdt)
> >+ return -ENOMEM;
> >+
> >+ platform_set_drvdata(pdev, wdt);
> >+
> >+ res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >+ wdt->base = devm_ioremap_resource(&pdev->dev, res);
> >+ if (IS_ERR(wdt->base))
> >+ return PTR_ERR(wdt->base);
> >+
> >+ ret = of_property_read_u32(pdev->dev.of_node, "clock-frequency", &tmp);
> >+ if (ret) {
> >+ dev_err(&pdev->dev, "unable to get clock-frequency\n");
> >+ return ret;
> >+ }
> >+
>
> You might want to use a clock property here, and the complete sequence of
> devm_clk_get
> clk_prepare_enable
> clk_disable_unprepare
> clk_get_rate

Agreed. I think this would be ideal. I'll need to take a closer look
at how this thing is clocked, and how/if the clocks are currently
being modelled.

> >+ wdt->freq = tmp;
> >+
> >+ wdt->wdd.dev = &pdev->dev;
> >+ wdt->wdd.info = &qcom_wdt_info;
> >+ wdt->wdd.ops = &qcom_wdt_ops;
> >+ wdt->wdd.min_timeout = 1;
> >+ wdt->wdd.max_timeout = 0x10000000U / wdt->freq;
>
> As written, wdt->freq can be 0, which results in a nice division by zero here.

Indeed. I'll add a check.

> >+ watchdog_init_timeout(&wdt->wdd, 0, &pdev->dev);
>
> That leaves you with no default timeout if timeout-sec is not set in devicetree,
> which if I understand the code correctly might result in an immediate reset.
> Is this really what you want to happen ?

I think I'd like to handle timeout-sec being unspecified as an error at
probe. If someone explicitly sets timeout-sec = <0>, then they get what
they ask for. I'll take another look to see how to make this happen.

> >+
> >+ ret = watchdog_register_device(&wdt->wdd);
> >+ if (ret) {
> >+ dev_err(&pdev->dev, "failed to register watchdog\n");
> >+ return ret;
> >+ }
> >+
> >+ return 0;
> >+}
> >+
> >+static const struct of_device_id qcom_wdt_of_table[] = {
> >+ { .compatible = "qcom,kpss-wdt-msm8960", },
> >+ { .compatible = "qcom,kpss-wdt-apq8064", },
> >+ { .compatible = "qcom,kpss-wdt-ipq8064", },
> >+ { },
> >+};
> >+MODULE_DEVICE_TABLE(of, qcom_wdt_of_table);
> >+
> >+static struct platform_driver qcom_watchdog_driver = {
> >+ .probe = qcom_watchdog_probe,
>
> No remove function ?
>
> Yes, you don't need it, because the driver can only be built into the kernel,
> but there is a practical impact: It means the driver must always be built
> into the kernel even if the image is supposed to be used on different systems,
> some of which may not support this specific watchdog.
>
> Sure, you might say that you don't care about images supporting more than one
> hardware, but the tendency seems to be multi-target images nowadays.

This was motivated by the addition of the restart_handler bits in patch
3. For some reason I was thinking there were race conditions between
module unloading/the restart_handler mechanism, but looking at it again,
I'm not so sure. Is it safe to implement these handlers in modules? If
so, I'll revisit this.

Thanks again,
Josh