Re: [PATCH] eeprom: at24: Support custom device names for AT24 EEPROMs

[Bartosz Golaszewski <bgolaszewski@baylibre.com>]

On Wed, Jun 2, 2021 at 7:08 PM Alexander Fomichev <fomichev.ru@gmail.com> wrote:
>
> On Thu, Sep 24, 2020 at 03:20:39PM +0200, Jon Hunter wrote:
> > By using the label property, a more descriptive name can be populated
> > for AT24 EEPROMs NVMEM device. Update the AT24 driver to check to see
> > if the label property is present and if so, use this as the name for
> > NVMEM device. Please note that when the 'label' property is present for
> > the AT24 EEPROM, we do not want the NVMEM driver to append the 'devid'
> > to the name and so the nvmem_config.id is initialised to
> > NVMEM_DEVID_NONE.
> >
> > Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> > index 2fde53dcfc97..4aa96d8e78ef 100644
> > --- a/drivers/misc/eeprom/at24.c
> > +++ b/drivers/misc/eeprom/at24.c
> > @@ -713,8 +713,28 @@ static int at24_probe(struct i2c_client *client)
> >                       return err;
> >       }
> >
> > +     /*
> > +      * If the 'label' property is not present for the AT24 EEPROM,
> > +      * then nvmem_config.id is initialised to NVMEM_DEVID_AUTO,
> > +      * and this will append the 'devid' to the name of the NVMEM
> > +      * device. This is purely legacy and the AT24 driver has always
> > +      * defaulted to this. However, if the 'label' property is
> > +      * present then this means that the name is specified by the
> > +      * firmware and this name should be used verbatim and so it is
> > +      * not necessary to append the 'devid'.
> > +      */
> > +     if (device_property_present(dev, "label")) {
> > +             nvmem_config.id = NVMEM_DEVID_NONE;
> > +             err = device_property_read_string(dev, "label",
> > +                                               &nvmem_config.name);
> > +             if (err)
> > +                     return err;
> > +     } else {
> > +             nvmem_config.id = NVMEM_DEVID_AUTO;
> > +             nvmem_config.name = dev_name(dev);
> > +     }
> > +
> >       nvmem_config.type = NVMEM_TYPE_EEPROM;
> > -     nvmem_config.name = dev_name(dev);
> >       nvmem_config.dev = dev;
> >       nvmem_config.id = NVMEM_DEVID_AUTO;
> >       nvmem_config.read_only = !writable;
>
> This change has a serious defect, as it doesn't guarantee a name
> uniqueness. For my case there are a bunch of NVMEM devices with
> 'dimm-spd' name. So the module initialization fails with several error
> dumps in dmesg, like following:
>
> [    4.784679] at24 3-0051: supply vcc not found, using dummy regulator
> [    4.784781] sysfs: cannot create duplicate filename '/bus/nvmem/devices/dimm-spd'
> [    4.784783] CPU: 24 PID: 1354 Comm: systemd-udevd Not tainted 5.13.0-rc4-at24-catch+ #25
> [    4.784787] Call Trace:
> [    4.784789] [c00000003f3eb010] [c000000000914700] dump_stack+0xc4/0x114 (unreliable)
> [    4.784797] [c00000003f3eb060] [c00000000061c5c8] sysfs_warn_dup+0x88/0xc0
> [    4.784803] [c00000003f3eb0e0] [c00000000061ccec] sysfs_do_create_link_sd+0x17c/0x190
> [    4.784809] [c00000003f3eb130] [c000000000ac3014] bus_add_device+0x94/0x1d0
> [    4.784817] [c00000003f3eb1b0] [c000000000abe7b8] device_add+0x428/0xb90
> [    4.784822] [c00000003f3eb2a0] [c000000000debbd0] nvmem_register+0x220/0xe00
> [    4.784829] [c00000003f3eb390] [c000000000dec80c] devm_nvmem_register+0x5c/0xc0
> [    4.784835] [c00000003f3eb3d0] [c008000016f40c20] at24_probe+0x668/0x940 [at24]
> [    4.784845] [c00000003f3eb650] [c000000000cfecd4] i2c_device_probe+0x194/0x650
> [    4.784850] [c00000003f3eb6f0] [c000000000ac4d3c] really_probe+0x1cc/0x790
> [    4.784855] [c00000003f3eb790] [c000000000ac545c] driver_probe_device+0x15c/0x200
> [    4.784861] [c00000003f3eb810] [c000000000ac5ecc] device_driver_attach+0x11c/0x130
> [    4.784866] [c00000003f3eb850] [c000000000ac5fd0] __driver_attach+0xf0/0x200
> [    4.784873] [c00000003f3eb8d0] [c000000000ac1158] bus_for_each_dev+0xa8/0x130
> [    4.784879] [c00000003f3eb930] [c000000000ac4104] driver_attach+0x34/0x50
> [    4.784885] [c00000003f3eb950] [c000000000ac35f0] bus_add_driver+0x1b0/0x2f0
> [    4.784893] [c00000003f3eb9e0] [c000000000ac70b4] driver_register+0xb4/0x1c0
> [    4.784900] [c00000003f3eba50] [c000000000cfe498] i2c_register_driver+0x78/0x120
> [    4.784905] [c00000003f3ebad0] [c008000016f41260] at24_init+0x6c/0x88 [at24]
> [    4.784914] [c00000003f3ebb30] [c0000000000122c0] do_one_initcall+0x60/0x2c0
> [    4.784920] [c00000003f3ebc00] [c0000000002537bc] do_init_module+0x7c/0x350
> [    4.784926] [c00000003f3ebc90] [c000000000257904] __do_sys_finit_module+0xd4/0x160
> [    4.784932] [c00000003f3ebdb0] [c00000000002c104] system_call_exception+0xf4/0x200
> [    4.784938] [c00000003f3ebe10] [c00000000000cf70] system_call_vectored_common+0xf0/0x268
> [    4.784944] --- interrupt: 3000 at 0x7c1adac4b4c4
> [    4.784948] NIP:  00007c1adac4b4c4 LR: 0000000000000000 CTR: 0000000000000000
> [    4.784951] REGS: c00000003f3ebe80 TRAP: 3000   Not tainted  (5.13.0-rc4-at24-catch+)
> [    4.784955] MSR:  900000000280f033 <SF,HV,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 48222844  XER: 00000000
> [    4.784976] IRQMASK: 0
>                GPR00: 0000000000000161 00007fffefc78b90 00007c1adad37000 0000000000000006
>                GPR04: 00000f6614d56be0 0000000000000000 0000000000000006 0000000000000000
>                GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>                GPR12: 0000000000000000 00007c1adafde680 0000000020000000 0000000000000000
>                GPR16: 0000000000000000 00000f66118b1980 00000f66118b1a18 00000f66118b1948
>                GPR20: 0000000000000000 00000f6614d60500 00007fffefc78df0 00000f6614d535c0
>                GPR24: 00000f6614d56be0 00000f6614d60500 000000000000000c 00000f6614d49cb0
>                GPR28: 00000f6614d56be0 0000000000020000 0000000000000000 00000f6614d60500
> [    4.785033] NIP [00007c1adac4b4c4] 0x7c1adac4b4c4
> [    4.785036] LR [0000000000000000] 0x0
> [    4.785040] --- interrupt: 3000
> [    4.785146] at24: probe of 3-0051 failed with error -17
>
>
> It needs either to use NVMEM_DEVID_AUTO flag irrespective of the 'label'
> property or to add a sort of counter suffix to the name field.
>
>
> Reported-by: Alexander Fomichev <fomichev.ru@gmail.com>
> CC: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>
> --
> Regards,
>   Alexander

Alexander: Thanks for your bug report. The counter suffix you suggest
is precisely what NVMEM_DEVID_AUTO would do so I think we'll need to
use it. On the other hand, a non-unique label is bad design but
obviously we can't break working setups.

Jon: As the author of this patch - do you have any objections/better ideas?

If not, I'll send out a fix soon.

Bart