linux-kernel - Re: [PATCH 1/1] drivers/misc: Add Intel System ID driver

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Date:   Wed, 1 Mar 2017 12:34:57 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "Loh, Tien Hock" <tien.hock.loh@...el.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Nguyen, Dinh" <dinh.nguyen@...el.com>,
        "thloh85@...il.com" <thloh85@...il.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Gerlach, Matthew" <matthew.gerlach@...el.com>
Subject: Re: [PATCH 1/1] drivers/misc: Add Intel System ID driver

On Wed, Mar 1, 2017 at 11:42 AM, Loh, Tien Hock <tien.hock.loh@...el.com> wrote:
> On Rab, 2017-03-01 at 10:01 +0100, Arnd Bergmann wrote:
>> On Wed, Mar 1, 2017 at 8:23 AM, Loh, Tien Hock <tien.hock.loh@...el.c
>> Another option would be to fold the timestamp into the revision
>> attribute,
>> but whether that is a reasonable place for it would in turn depend on
>> what the timestamp signifies.
>>
>> Can you explain what the timestamp is used for? Does it identify the
>> time that the hardware revision was made, the time that a software
>> was built which was loaded into it, or something else?
>> What kind of user space application would need this information?
>
> I just checked, and it seems like we can't put this into soc subsystem.
> In FPGA, we now can do partial reconfiguration, which "reconfigures"
> the hardware to have an updated sysid and timestamp value, and the base
> address of the Intel System ID may also be changed. This would require
> the driver to be a module that will be removed, probed again. The soc
> subsystem doesn't seem to be a suitable place to add this driver.

Ah, I had not realized this is for fpga_manager.

Why not put the attributes into /sys/class/fpga_manager/*/ then
along with the other attributes that exist there? That way, we have
an interface that works for all users of drivers/fpga/

> A note on the timestamp, in the old days this is used to check that the
> BSP is using the correct FPGA hardware. I believe in Linux we should do
> the same in the driver, and if it not, the driver should print a
> warning. The timestamp's print is not exactly needed. I'll add the
> feature into the driver in the next patch.

Ok.

     Arnd