[PATCH 6/9] rtc: stmp3xxx: add sysfs entries for persistent regs

[Grant Likely]

On Mon, Mar 4, 2013 at 10:05 PM, Steffen Trumtrar
<s.trumtrar at pengutronix.de> wrote:
> The persistent registers 1-5 are completely software defined. To have access
> from userspace, export them via sysfs.
>
> Signed-off-by: Steffen Trumtrar <s.trumtrar at pengutronix.de>

Hi Steffen,

A few comments on this. First and foremost, any additions to the
kernel sysfs interface must be accompanied with documentation in
Documentation/ABI/. Second, adding attributes to an existing device
that has already been registered is almost guaranteed to be wrong. The
attributes need to be added all at the same time so they are available
immediately when the new device uevent is issued by the kernel.

Instead, the correct thing to do is add an attribute_group to the
child device before the device gets registered. See the 'attributes'
section of Documentation/driver-model/device.txt to see how to do
this.

(I also see that the rtc core code is doing the wrong thing here also.
rtc_sysfs_add_device(), rtc_sysfs_add_device() should also be replaced
with an attribute group so that the sysfs files get added
automatically; but that is outside the scope of this patch)

g.

> ---
>  drivers/rtc/rtc-stmp3xxx.c |   69 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 69 insertions(+)
>
> diff --git a/drivers/rtc/rtc-stmp3xxx.c b/drivers/rtc/rtc-stmp3xxx.c
> index 936b0ca..16b45c8 100644
> --- a/drivers/rtc/rtc-stmp3xxx.c
> +++ b/drivers/rtc/rtc-stmp3xxx.c
> @@ -67,6 +67,8 @@
>  /* missing bitmask in headers */
>  #define STMP3XXX_RTC_PERSISTENT1_FORCE_UPDATER 0x80000000
>
> +#define STMP3XXX_RTC_PERSISTENT_LEN            (0xC0 - STMP3XXX_RTC_PERSISTENT1)
> +
>  enum clock_source { MXS_UNKNOWN, MXS_OSC_24M, MXS_OSC_32K, MXS_OSC_32K768 };
>
>  struct stmp3xxx_rtc_data {
> @@ -74,6 +76,9 @@ struct stmp3xxx_rtc_data {
>         void __iomem *io;
>         int irq_alarm;
>         enum clock_source clk_src;
> +#if IS_ENABLED(CONFIG_RTC_INTF_SYSFS)
> +       struct bin_attribute *persist;
> +#endif
>  };
>
>  #if IS_ENABLED(CONFIG_STMP3XXX_RTC_WATCHDOG)
> @@ -262,6 +267,42 @@ static int stmp3xxx_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
>         return 0;
>  }
>
> +#if IS_ENABLED(CONFIG_RTC_INTF_SYSFS)
> +static ssize_t stmp3xxx_rtc_persist_read(struct file *filep,
> +                                        struct kobject *kobj,
> +                                        struct bin_attribute *bin_attr,
> +                                        char *buf, loff_t off, size_t size)
> +{
> +       struct rtc_device *rtc = container_of(kobj, struct rtc_device,
> +                                             dev.kobj);
> +       struct device *dev = rtc->dev.parent;
> +       struct stmp3xxx_rtc_data *rtc_data = dev_get_drvdata(dev);
> +       ssize_t count;
> +
> +       for (count = 0; size; size--, off++, count++)
> +               *buf++ = readl(rtc_data->io + STMP3XXX_RTC_PERSISTENT1 + off);
> +
> +       return count;
> +}
> +
> +static ssize_t stmp3xxx_rtc_persist_write(struct file *filep,
> +                                         struct kobject *kobj,
> +                                         struct bin_attribute *bin_attr,
> +                                         char *buf, loff_t off, size_t size)
> +{
> +       struct rtc_device *rtc = container_of(kobj, struct rtc_device,
> +                                             dev.kobj);
> +       struct device *dev = rtc->dev.parent;
> +       struct stmp3xxx_rtc_data *rtc_data = dev_get_drvdata(dev);
> +       ssize_t count;
> +
> +       for (count = 0; size; size--, off++, count++)
> +               writel(*buf++, rtc_data->io + STMP3XXX_RTC_PERSISTENT1 + off);
> +
> +       return count;
> +}
> +#endif
> +
>  static struct rtc_class_ops stmp3xxx_rtc_ops = {
>         .alarm_irq_enable =
>                           stmp3xxx_alarm_irq_enable,
> @@ -278,6 +319,11 @@ static int stmp3xxx_rtc_remove(struct platform_device *pdev)
>         if (!rtc_data)
>                 return 0;
>
> +#if IS_ENABLED(CONFIG_RTC_INTF_SYSFS)
> +       sysfs_remove_bin_file(&pdev->dev.kobj, rtc_data->persist);
> +       kfree(rtc_data->persist);
> +#endif
> +
>         writel(STMP3XXX_RTC_CTRL_ALARM_IRQ_EN,
>                         rtc_data->io + STMP3XXX_RTC_CTRL_CLR);
>         free_irq(rtc_data->irq_alarm, &pdev->dev);
> @@ -384,8 +430,31 @@ static int stmp3xxx_rtc_probe(struct platform_device *pdev)
>         }
>
>         stmp3xxx_wdt_register(pdev);
> +
> +#if IS_ENABLED(CONFIG_RTC_INTF_SYSFS)
> +       rtc_data->persist = kzalloc(sizeof(struct bin_attribute), GFP_KERNEL);
> +       if (!rtc_data->persist) {
> +               err = -ENOMEM;
> +               goto out_persist;
> +       }
> +
> +       rtc_data->persist->attr.name = "persistent";
> +       rtc_data->persist->attr.mode = S_IRUGO | S_IWUSR;
> +       sysfs_bin_attr_init(rtc_data->persist);
> +       rtc_data->persist->read = stmp3xxx_rtc_persist_read;
> +       rtc_data->persist->write = stmp3xxx_rtc_persist_write;
> +       rtc_data->persist->size = STMP3XXX_RTC_PERSISTENT_LEN;
> +       err = sysfs_create_bin_file(&rtc_data->rtc->dev.kobj,
> +                               rtc_data->persist);
> +       if (err) {
> +               kfree(rtc_data->persist);
> +               goto out_persist;
> +       }
> +#endif
> +
>         return 0;
>
> +out_persist:
>  out_irq_alarm:
>         rtc_device_unregister(rtc_data->rtc);
>  out_remap:
> --
> 1.7.10.4
>
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--
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.