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Subject: Re: [PATCH 1/5] misc: eeprom: at24: Initialise AT24 NVMEM ID field
From:   Jon Hunter <jonathanh@nvidia.com>
To:     Bartosz Golaszewski <bgolaszewski@baylibre.com>
CC:     Rob Herring <robh+dt@kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        linux-i2c <linux-i2c@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-devicetree <devicetree@vger.kernel.org>,
        <linux-tegra@vger.kernel.org>
References: <20200910134239.192030-1-jonathanh@nvidia.com>
 <20200910134239.192030-2-jonathanh@nvidia.com>
 <CAMpxmJXbhrmJJn4f3zk4=Y2tCwLzpFc+c6NbxcqVe8eaLSRvtw@mail.gmail.com>
 <88021f57-b8cf-d3d6-0e9c-19ed0bccb729@nvidia.com>
Message-ID: <5afe9537-dc50-16ff-028e-b4539c6f924a@nvidia.com>
Date:   Thu, 10 Sep 2020 19:19:14 +0100
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On 10/09/2020 19:15, Jon Hunter wrote:
> 
> On 10/09/2020 16:35, Bartosz Golaszewski wrote:
>> On Thu, Sep 10, 2020 at 3:43 PM Jon Hunter <jonathanh@nvidia.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@nvidia.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.


Unless we make the configuration of the 'id' dependent on the 'label'
property so something like ...

	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);
	}

Cheers
Jon

-- 
nvpublic