[U-Boot] [EXT] Re: [PATCH] i2c: pcf2127: fix bug that read wrong time

Lukasz Majewski
2019-05-23T05:54:20Z

Hi Heiko,

> Hello Chuanhua Han,
>
> Am 22.05.2019 um 14:45 schrieb Chuanhua Han:
> >
> >
> >> -----Original Message-----
> >> From: Lukasz Majewski <lukma@denx.de>
> >> Sent: 2019年5月22日 19:32
> >> To: Chuanhua Han <chuanhua.han@nxp.com>
> >> Cc: hs at denx.de; u-boot at lists.denx.de; Biwen Li <biwen.li@nxp.com>;
> >> sjg at chromium.org; Stefano Babic <sbabic@denx.de>
> >> Subject: Re: [EXT] Re: [PATCH] i2c: pcf2127: fix bug that read
> >> wrong time
> >>
> >> On Wed, 22 May 2019 09:31:35 +0000
> >> Chuanhua Han <chuanhua.han@nxp.com> wrote:
> >>
> >>>> -----Original Message-----
> >>>> From: Lukasz Majewski <lukma@denx.de>
> >>>> Sent: 2019年5月22日 16:41
> >>>> To: Chuanhua Han <chuanhua.han@nxp.com>
> >>>> Cc: hs at denx.de; u-boot at lists.denx.de; Biwen Li
> >>>> <biwen.li@nxp.com>; sjg at chromium.org; Stefano Babic
> >>>> <sbabic@denx.de> Subject: Re: [EXT] Re: [PATCH] i2c: pcf2127:
> >>>> fix bug that read wrong time
> >>>>
> >>>> Hi Chuanhua,
> >>>>
> >>>>>> -----Original Message-----
> >>>>>> From: Lukasz Majewski <lukma@denx.de>
> >>>>>> Sent: 2019年5月22日 15:16
> >>>>>> To: Chuanhua Han <chuanhua.han@nxp.com>
> >>>>>> Cc: hs at denx.de; u-boot at lists.denx.de; Biwen Li
> >>>>>> <biwen.li@nxp.com>; sjg at chromium.org
> >>>>>> Subject: [EXT] Re: [PATCH] i2c: pcf2127: fix bug that read
> >>>>>> wrong time
> >>>>>>
> >>>>>> Hi Chuanhua,
> >>>>>>
> >>>>>>> Because i2c driver does not generate a stop bit when reading
> >>>>>>> registers of pcf2127
> >>>>>>
> >>>>>> The change (in the common i2c code) is rather large when
> >>>>>> considering the description above.
> >>>>>>
> >>>>>> Could you write a more detailed patch description? Is this only
> >>>>>> the problem with i2c in DM?
> >>>>> OK, This is a problem with the i2c transport framework. After
> >>>>> writing the register address that you want to read, the stop
> >>>>> signal is missing before reading the register data.
> >>>>>>
> >>>>>> Is the same code (as introduced in this commit) available in
> >>>>>> Linux kernel?
> >>>>> The kernel does not have such a problem
> >>>>
> >>>> Do you know maybe why such issue is not present on Linux
> >>>> kernel?
> >>> The kernel code is encapsulated when reading the pcf2127 register,
> >>> which separates the read and write, thus generating a stop signal
> >>> before reading the register. Eg: Here is the wrapper made by the
> >>> kernel code: static int pcf2127_i2c_read(void *context, const void
> >>> *reg, size_t reg_size, void *val, size_t val_size) {
> >>> struct device *dev = context;
> >>> struct i2c_client *client = to_i2c_client(dev);
> >>> int ret;
> >>>
> >>> if (WARN_ON(reg_size != 1))
> >>> return -EINVAL;
> >>>
> >>> ret = i2c_master_send(client, reg, 1);
> >>> if (ret != 1)
> >>> return ret < 0 ? ret : -EIO;
> >>>
> >>> ret = i2c_master_recv(client, val, val_size);
> >>> if (ret != val_size)
> >>> return ret < 0 ? ret : -EIO;
> >>>
> >>> return 0;
> >>> }
> >>
> >> That was my point - the same shall be done in the pcf2127 driver.
> >> This is a slow device, so we can afford for this.
> > There is no similar api in the uboot code to split the read data
> > into the address of the send register and receive the data. Uboot
> > encapsulates the transmit register address and the read data, so no
> > stop signal is generated.
>
> If this API is missing, please introduce it. But not in one big patch
> instead split it into:
>
> - introduce I2C_M_RD_NEED_STOP_BIT
>
> - support flag I2C_M_RD_NEED_STOP_BIT in driver drivers/i2c/mxc_i2c.c
>
> or may we need a more common approach to this?
>
> - pcf2127 driver changes
>
> Also, as Lukasz mentioned, provide commit messages with more
> information, what you do and why.

Verbose commit messages help with understanding the _real_ problem
being solved by the patch. Also are helpful in the future as a
documentation and reference.

>
> >>
> >>>>
> >>>>>> How the error is reproduced? What are the symptoms of it?
> >>>>> You can use the i2c command to read the register data of
> >>>>> pcf2127.
> >>>>
> >>>> So the problem is with using "i2c ..." commands from U-Boot
> >>>> prompt?
> >>> Yes,but adding debugging to the rtc driver is also the same
> >>> problem
> >>>>
> >>>>> You will find that you want to read the address 0 of the
> >>>>> register, but the data of the 1 address is read, and the data
> >>>>> read later will be offset.
> >>>>
> >>>> As fair as I can tell the pcf2127 has its own DM aware driver at
> >>>> driver/rtc/pcf2127.c.
> >>>>
> >>>> Is this driver broken so you need to modify the generic i.MX I2C
> >>>> code? Have you tried to test this driver on your setup?
> >>> Pcf2127 driver also has problems, has been modified, need i2c
> >>> general code to support
> >>
> >> Just one remark the mxc_i2c.c is IMX specific I2C code. Not the
> >> generic one.
> > ok
> >>
> >> Moreover, it looks like the same approach (first send, then read)
> >> is performed in the pcf2127 driver at pcf2127_rtc_get() function.
> >>
> >> I think that the driver shall be first thoroughly checked, then
> >> fixes shall be added to it.
>
> I have no such device, so hard to say ... and as Lukasz alread
> mentioned the driver seems to make such an approach:
>
> 52 static int pcf2127_rtc_get(struct udevice *dev, struct rtc_time
> *tm) 53 {
> 54 int ret = 0;
> 55 uchar buf[10] = { PCF2127_REG_CTRL1 };
> 56
> 57 ret = dm_i2c_write(dev, PCF2127_REG_CTRL1, buf, 1);
> 58 if (ret < 0)
> 59 return ret;
> 60 ret = dm_i2c_read(dev, PCF2127_REG_CTRL1, buf,
> sizeof(buf)); 61 if (ret < 0)
> 62 return ret;
>

I would prefer to fix the issue in the driver itself. Only when it is
not possible we shall introduce extra flags and modify the common I2C
code.

>
> It seems there are currently no real users of this driver:
>
> pollux:u-boot hs [master] $ grep -lr RTC_PCF2127 .
> ./drivers/rtc/Kconfig
> ./drivers/rtc/Makefile
> pollux:u-boot hs [master] $
>
> I added Meng Yi to cc, as he is the author of this driver. May he
> can say here more... at last I hope, the driver worked for him.
>
> bye,
> Heiko

Best regards,

Lukasz Majewski

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