linux-kernel - Re: [RFC PATCH 5/8] qaic: Implement data path

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Date:   Thu, 14 May 2020 10:45:50 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     arnd@...db.de, manivannan.sadhasivam@...aro.org,
        bjorn.andersson@...aro.org, wufan@...eaurora.org,
        pratanan@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/8] qaic: Implement data path

On 5/14/2020 10:37 AM, Greg KH wrote:
> On Thu, May 14, 2020 at 10:12:03AM -0600, Jeffrey Hugo wrote:
>> On 5/14/2020 9:56 AM, Greg KH wrote:
>>> On Thu, May 14, 2020 at 09:06:53AM -0600, Jeffrey Hugo wrote:
>>>> On 5/14/2020 8:14 AM, Greg KH wrote:
>>>>> On Thu, May 14, 2020 at 08:07:43AM -0600, Jeffrey Hugo wrote:
>>>>>> +struct qaic_execute {
>>>>>> +	__u16		ver;    /* struct version, must be 1 */
>>>>>
>>>>> No need for structures to be versioned.  If you change something, then
>>>>> add a new ioctl if you really needed it.
>>>>
>>>> Huh.  We had thought the botching ioctls document advised having a version,
>>>> but as I double check that document, it infact does not.
>>>>
>>>> Will remove.
>>>
>>> Thanks, you can also remove the "reserved" variables as well as those
>>> will not be needed either.
>>
>> Are you sure?
>>
>> Documentation/process/botching-up-ioctls.rst
>> Starting at Line 38:
>>
>> "Pad the entire struct to a multiple of 64-bits if the structure contains
>> 64-bit types - the structure size will otherwise differ on 32-bit versus
>> 64-bit. Having a different structure size hurts when passing arrays of
>> structures to the kernel, or if the kernel checks the structure size, which
>> e.g. the drm core does."
>>
>> The "reserved" variables seem to be in line with that.
> 
> Padding is fine to use, but don't use that as a "I'm reserving this to
> use it for later" type of thing which is how I read the structure
> definitions.  I might be totally wrong, but you should be explicit here.

Ok, I think I see your point.  I'll change them to be more explicit as 
padding.

-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.