linux-kernel - Re: [PATCH 1/5] misc: eeprom: at24: Initialise AT24 NVMEM ID field

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Date:   Thu, 10 Sep 2020 19:15:35 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 1/5] misc: eeprom: at24: Initialise AT24 NVMEM ID field


On 10/09/2020 16:35, Bartosz Golaszewski wrote:
> On Thu, Sep 10, 2020 at 3:43 PM Jon Hunter <jonathanh@...dia.com> wrote:
>>
>> The AT24 EEPROM driver does not initialise the 'id' field of the
>> nvmem_config structure and because the entire structure is not
>> initialised, it ends up with a random value. This causes the NVMEM
>> driver to append the device 'devid' value to name of the NVMEM
>> device. Although this is not a problem per-se, for I2C devices such as
>> the AT24, that already have a device unique name, there does not seem
>> much value in appending an additional 0 to the I2C name. For example,
>> appending a 0 to an I2C device name such as 1-0050 does not seem
>> necessary and maybe even a bit confusing. Therefore, fix this by
>> setting the NVMEM config.id to NVMEM_DEVID_NONE for AT24 EEPROMs.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>> ---
>>  drivers/misc/eeprom/at24.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
>> index e9df1ca251df..3f7a3bb6a36c 100644
>> --- a/drivers/misc/eeprom/at24.c
>> +++ b/drivers/misc/eeprom/at24.c
>> @@ -715,6 +715,7 @@ static int at24_probe(struct i2c_client *client)
>>
>>         nvmem_config.name = dev_name(dev);
>>         nvmem_config.dev = dev;
>> +       nvmem_config.id = NVMEM_DEVID_NONE;
>>         nvmem_config.read_only = !writable;
>>         nvmem_config.root_only = !(flags & AT24_FLAG_IRUGO);
>>         nvmem_config.owner = THIS_MODULE;
>> --
>> 2.25.1
>>
> 
> This patch is correct and thanks for catching it. I vaguely recall
> wondering at some point why the appended 0 in the nvmem name for at24.
> Unfortunately this change would affect how the device is visible in
> user-space in /sys/bus/nvmem/devices/ and this could break existing
> users. Also: there are many in-kernel users that would need to be
> updated. I'm afraid we'll need some sort of backward compatibility.


Thanks, yes that is a problem. I guess for now we could explicitly init
to NVMEM_DEVID_AUTO or maybe just 0 so that it defaults to the same path
in the NVMEM driver. However, I am not sure how we can make allow some
devices to use NVMEM_DEVID_NONE and others use something else. This is
not really something that we can describe in DT because it has nothing
to do with h/w.

Cheers
Jon

-- 
nvpublic