linux-kernel - Re: [discuss] Improve and merge a driver proposed in 2013: sysfs interfaces to access TXT config space

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Date:   Thu, 17 Feb 2022 13:37:53 +0100
From:   Pavel Machek <pavel@....cz>
To:     "greg@...ah.com" <greg@...ah.com>
Cc:     Dmitrii Okunev <xaionaro@...com>,
        "qiaowei.ren@...el.com" <qiaowei.ren@...el.com>,
        "matthew.garrett@...ula.com" <matthew.garrett@...ula.com>,
        "xiaoyan.zhang@...el.com" <xiaoyan.zhang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "gang.wei@...el.com" <gang.wei@...el.com>,
        Jonathan McDowell <noodles@...com>
Subject: Re: [discuss] Improve and merge a driver proposed in 2013: sysfs
 interfaces to access TXT config space

On Thu 2022-02-17 13:34:40, greg@...ah.com wrote:
> On Thu, Feb 17, 2022 at 11:47:21AM +0000, Dmitrii Okunev wrote:
> > Hello!
> > 
> > As far as I see the patch wasn't merged. And I see that this is the
> > only unsolved thread in the discussion:
> > 
> > On Thu, 2013-05-16 at 18:03 +0200, Pavel Machek wrote:
> > > On Tue 2013-05-14 01:24:43, Qiaowei Ren wrote:
> > > > These interfaces are located in
> > > > /sys/devices/platform/intel_txt/config,
> > > > and including totally 37 files, providing access to Intel TXT
> > > > configuration registers.
> > > 
> > > This looks like very wrong interface... equivalent of /dev/mem.
> > 
> > As an active user of these registers I hope it will be merged, so I
> > would like to improve this patch (or rewrite it from scratch) to make
> > that happen. Otherwise one have to do hackery around `/dev/mem`, which
> > also creates problems with proper access control.
> > 
> > To be able to improve the patch, could somebody clarify why exactly
> > this is a "very wrong interface"?
> > 
> > > > +What:          /sys/devices/platform/intel_txt/config/STS_raw
> > > > +Date:          May 2013
> > > > +KernelVersion: 3.9
> > > > +Contact:       "Qiaowei Ren" <qiaowei.ren@...el.com>
> > > > +Description:   TXT.STS is the general status register. This read-
> > > > only register
> > > > +               is used by AC modules and the MLE to get the status
> > > > of various
> > > > +               Intel TXT features.
> > > 
> > > This is not enough to allow people to understand what this
> > > does/should
> > > do, nor does it allow (for example) ARM people to implement something
> > > compatible.
> > > 
> > > Is there specific reason why "better" interface is impossible?
> > 
> > I would love to reuse Intel's public documentation [1] to provide a
> > proper description (with bit layout of the value).
> > 
> > [1] https://cdrdv2.intel.com/v1/dl/getContent/315168
> > 
> > > [...], nor does it allow (for example) ARM people to
> > > implement something compatible.
> > 
> > Do I understand correctly that a proper documentation of the registers
> > solves the problem?
> > 
> > > Is there specific reason why "better" interface is impossible?
> > 
> > What are specific problems with the current interface?
> 
> What do you mean by "current" here?  You are referring to an email from
> 2013, 9 years ago.
> 
> If you want to propose the change again, correctly update the patch and
> submit it that way.

I don't believe taking hardware registers and exposing them 1-to-1 in
sysfs is the way to go.

We would like same /sys interface on different hardware, and simply
exposing Intel's registers in /sys will not do the job.

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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