Re: Re: [PATCH] rtc: rs5c372: Fix read the time from RTC is illegal When reading time from an uninitialized RTC chip, The value may be illegal

[Alexandre Belloni]

Hi,

On 25/05/2021 19:24:14+0800, qxj511mail@xxxxxxxxx wrote:
> Please briefly describe the patch contained in the email to the subject.
> And, please write a description of the patch in the text
> ---->   The legal days are 1 to 31 and the legal month is less than or equal to 12.
>            But for an uninitialized RTC chip, the time is random.
>            Days and month may be zero, leading to RTC_valid_TM failed
> 

If the time on the RTC is invalid, then rtc_valid_tm has to fail, there
is nothing to fix here.

> add description  && fix build error, so I modefied my code :
>  
> Signed-off-by: qiuxiaojin <qiuxiaojin@xxxxxxxx>
> ---
>  drivers/rtc/rtc-rs5c372.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
> index 3bd6eaa0dcf6..cb3f90983778 100644
> --- a/drivers/rtc/rtc-rs5c372.c
> +++ b/drivers/rtc/rtc-rs5c372.c
> @@ -128,6 +128,9 @@ struct rs5c372 {
>   char *regs;
>  };
>  
> +
> +static int rs5c372_rtc_set_time(struct device *dev, struct rtc_time *tm);
> +
>  static int rs5c_get_regs(struct rs5c372 *rs5c)
>  {
>   struct i2c_client *client = rs5c->client;
> @@ -212,6 +215,7 @@ static int rs5c372_rtc_read_time(struct device *dev, struct rtc_time *tm)
>   struct rs5c372 *rs5c = i2c_get_clientdata(client);
>   int status = rs5c_get_regs(rs5c);
>   unsigned char ctrl2 = rs5c->regs[RS5C_REG_CTRL2];
> + int flags_utime = 0;
>  
>   if (status < 0)
>   return status;
> @@ -239,12 +243,28 @@ static int rs5c372_rtc_read_time(struct device *dev, struct rtc_time *tm)
>   tm->tm_wday = bcd2bin(rs5c->regs[RS5C372_REG_WDAY] & 0x07);
>   tm->tm_mday = bcd2bin(rs5c->regs[RS5C372_REG_DAY] & 0x3f);
>  
> + /* The value read from the register may be zero, which is an illegal value */
> + if (tm->tm_mday < 1) {
> + flags_utime++;
> + tm->tm_mday = 1;
> + }
> +
>   /* tm->tm_mon is zero-based */
>   tm->tm_mon = bcd2bin(rs5c->regs[RS5C372_REG_MONTH] & 0x1f) - 1;
>  
> + if (tm->tm_mon < 0) {
> + /* avoid illegal month */
> + flags_utime++;
> + tm->tm_mon = 0;
> + }
> +
>   /* year is 1900 + tm->tm_year */
>   tm->tm_year = bcd2bin(rs5c->regs[RS5C372_REG_YEAR]) + 100;
>  
> + /* update legal time */
> + if (flags_utime > 0)
> + rs5c372_rtc_set_time(dev, tm);
> +
>   dev_dbg(&client->dev, "%s: tm is secs=%d, mins=%d, hours=%d, "
>   "mday=%d, mon=%d, year=%d, wday=%d\n",
>   __func__,
> -- 
> 2.29.0
> 
> 
> 
> qxj511mail@xxxxxxxxx
>  
> From: Nobuhiro Iwamatsu
> Date: 2021-05-24 12:40
> To: qxj511mail
> CC: Alessandro Zummo; Alexandre Belloni; linux-rtc; Linux Kernel Mailing List; qiuxiaojin
> Subject: Re: [PATCH] rtc: rs5c372: Fix read the time from RTC is illegal When reading time from an uninitialized RTC chip, The value may be illegal
> Hi,
>  
> 2021年5月20日(木) 12:32 <qxj511mail@xxxxxxxxx>:
> >
> > From: qiuxiaojin <qiuxiaojin@xxxxxxxx>
>  
> Please briefly describe the patch contained in the email to the subject.
> And, please write a description of the patch in the text
>  
> >
> > Signed-off-by: qiuxiaojin <qiuxiaojin@xxxxxxxx>
> > ---
> >  drivers/rtc/rtc-rs5c372.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
> > index 3bd6eaa0dcf6..ce61e15d5f3a 100644
> > --- a/drivers/rtc/rtc-rs5c372.c
> > +++ b/drivers/rtc/rtc-rs5c372.c
> > @@ -212,6 +212,7 @@ static int rs5c372_rtc_read_time(struct device *dev, struct rtc_time *tm)
> >         struct rs5c372  *rs5c = i2c_get_clientdata(client);
> >         int             status = rs5c_get_regs(rs5c);
> >         unsigned char ctrl2 = rs5c->regs[RS5C_REG_CTRL2];
> > +       int flags_utime = 0;
> >
> >         if (status < 0)
> >                 return status;
> > @@ -239,12 +240,27 @@ static int rs5c372_rtc_read_time(struct device *dev, struct rtc_time *tm)
> >         tm->tm_wday = bcd2bin(rs5c->regs[RS5C372_REG_WDAY] & 0x07);
> >         tm->tm_mday = bcd2bin(rs5c->regs[RS5C372_REG_DAY] & 0x3f);
> >
> > +       if (tm->tm_mday < 1) {
> > +               // The value read from the register may be zero, which is an illegal value
>  
> Please use C89 style commet (/* */).
>  
> > +               flags_utime = flags_utime + 1;
>  
> I like using ++ (flags_utime++).
>  
> > +               tm->tm_mday = 1;
> > +       }
> > +
> >         /* tm->tm_mon is zero-based */
> >         tm->tm_mon = bcd2bin(rs5c->regs[RS5C372_REG_MONTH] & 0x1f) - 1;
> >
> > +       if (tm->tm_mon < 0) {
> > +               flags_utime = flags_utime + 1;
> > +               tm->tm_mday = 0;
> > +       }
> > +
> >         /* year is 1900 + tm->tm_year */
> >         tm->tm_year = bcd2bin(rs5c->regs[RS5C372_REG_YEAR]) + 100;
> >
> > +       if (flags_utime > 0) {
>  
> {} is unnecessary.
>  
> > +               rs5c372_rtc_set_time(dev, tm);
>  
> A build error will occur because there is no declaration of
> rs5c372_rtc_set_time.
> Please make sure this can be compiled.
>  
> > +       }
> > +
> >         dev_dbg(&client->dev, "%s: tm is secs=%d, mins=%d, hours=%d, "
> >                 "mday=%d, mon=%d, year=%d, wday=%d\n",
> >                 __func__,
> > --
> > 2.29.0
> >
>  
>  
> -- 
> Nobuhiro Iwamatsu
>    iwamatsu at {nigauri.org / debian.org}
>    GPG ID: 40AD1FA6



-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com