Message-ID: <1bd48029-9acd-dca5-c05e-3a657122546d@codeaurora.org>
Date:   Tue, 26 Mar 2019 18:44:04 +0530
From:   Gaurav Kohli <gkohli@...eaurora.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-kernel@...r.kernel.org
Cc:     linux-arm-msm@...r.kernel.org,
        Shiraz Hashim <shashim@...eaurora.org>
Subject: Re: [PATCH v0] nvmem: core: Export nvmem cell info to userspace


On 3/25/2019 4:28 PM, Srinivas Kandagatla wrote:
>
>
> On 24/03/2019 15:25, Gaurav Kohli wrote:
>>
>> On 3/22/2019 8:53 PM, Srinivas Kandagatla wrote:
>>>
>>>
>>> On 20/03/2019 05:53, Gaurav Kohli wrote:
>>>> From: Shiraz Hashim <shashim@...eaurora.org>
>>>>
>>>> Existing nvmem framework export full register space
>>>> as nvmem binary, but not exporting child node of nvmem
>>>> which is nvmem cell. Kernel can read the specific cell
>>>> by using nvmem_cell_read but userspace don't have such
>>>> provision.
>>>>
>>>> Add framework to export nvmem cell as well, So
>>>> userspace can use it directly.
>>>>
>>>> Signed-off-by: Shiraz Hashim <shashim@...eaurora.org>
>>>> Signed-off-by: Gaurav Kohli <gkohli@...eaurora.org>
>>>> Co-developed-by: Gaurav Kohli <gkohli@...eaurora.org>
>>>>
>>>> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
>>>
>>> Thankyou for the patch.
>>>
>>> Why do you need such provision when the userspace can just get the 
>>> cell values using correct offset and size.
>>> This will also bring over head of managing entries dynamically + 
>>> confusing userspace abi.
>>>
>>> Unless you have a valid reason or usecase I don't see the need for 
>>> this.
>>
>>
>> Hi Srinivas,
>>
>>
>> This is mainly for user space convenience, In existing implementation 
>> they have to do manipulation according
>
>>
>> to offset and bit, And with present patch, they just have to do cat 
>> for cell name and which can also be easily maintainable
> Yes, that is expected I guess!
>
>>
>> for different soc. But with current, it is difficult to maintain 
>> users space code as each time we have to change user space code 
>> according to bit.
>
> Which user space code/application are you referring to here? Are these 
> open source?

Hi Srini,

This is not open source, we have a requirement to read certain bits of 
nvmem.

>
>>
>>
>> This would also help to expose certain bit only as per the bit 
>> parameter mentioned in dt node, which would also help to protect 
>> exposing of
>>
> NVMEM is not just limited for DT users, non dt users use this f/w too.
> So the problem is not as simple as it sounds.
>
> If your issue is just about DT, you could easily parse active device 
> tree via  /proc/device-tree and get cell offset, length and names from 
> it, use this information to read from nvmem.
>
> There are other concerns about the userspace ABI w.r.t udev events.
> udev events would race with the creation on this cell entries 
> resulting in a behavior where user-space applications would not see 
> the entries after udev events.
>
> In worst case if we decide to go with adding cells to nvmem then we 
> should do it before the device is even probed using group attributes.
> And this would mean that we can not support cells that are dynamically 
> defined. And there might be some memory freeing issues in this method 
> too!
yes i agree they are dynamic entries as well of nvmem cell,  Can you 
please suggest some other way ?
>
> --srini
>
>
>> other bits to user space.
>>
>>>
>>> thanks,
>>> srini
>>
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