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

Chuanhua Han
2019-05-23T10:28:38Z

> -----Original Message-----
> From: Lukasz Majewski <lukma@denx.de>
> Sent: 2019年5月23日 13:54
> To: Heiko Schocher <hs@denx.de>
> Cc: Chuanhua Han <chuanhua.han@nxp.com>; u-boot at lists.denx.de; Biwen Li
> <biwen.li@nxp.com>; sjg at chromium.org; Stefano Babic <sbabic@denx.de>;
> Meng Yi <meng.yi@nxp.com>
> Subject: Re: [EXT] Re: [PATCH] i2c: pcf2127: fix bug that read wrong time
>
> 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.
I'll sort out the details in the next patch
>
> >
> > >>
> > >>>>
> > >>>>>> 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.
Because the pcf2127 chip is special, it must have a stop signal after writing
the register to perform the following operations of reading the register.

/***********************
*Generate the first part timings of reading from registers.
* write bit STOP
* | |
* ----------------------------------------------------------------------------------------------------------------
* | S | 1 0 1 0 0 0 1 0 | A | 00h-1Dh | A | P |
* ----------------------------------------------------------------------------------------------------------------
* | slave address = 0x51 | | | register address | |
* | |
* ACK from slave ACK from slave
**/
ret = dm_i2c_write(dev, PCF2127_REG_CTRL1, buf, 0);
if (ret < 0)
return ret;

/***********************
*Generate the second part timings of reading from registers.
* read bit STOP
* | |
* ----------------------------------------------------------------------------------------------------------------------------------------------------------
* | S | 1 0 1 0 0 0 1 1 | A | data byte(0-n) | A | last data byte | NA | P |
* ------------------------------------------------------------------------------------------------------------------------------------------------------------
* |slave address = 0x51 | | | data from slave | | |
* | | |
* ACK from slave ACK from master No ACK
*/
ret = dm_i2c_read(dev, PCF2127_REG_CTRL1, buf, sizeof(buf));
if (ret < 0)
return ret;>
> >
> > 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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