linux-kernel - Re: [PATCH v3 2/2] scsi: ufs: Add HCI capabilities sysfs group

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Message-ID: <20240811130221.GA2809@thinkpad>
Date: Sun, 11 Aug 2024 18:32:21 +0530
From: Manivannan Sadhasivam <manisadhasivam.linux@...il.com>
To: Avri Altman <Avri.Altman@....com>
Cc: "Martin K . Petersen" <martin.petersen@...cle.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bart Van Assche <bvanassche@....org>,
	Keoseong Park <keosung.park@...sung.com>
Subject: Re: [PATCH v3 2/2] scsi: ufs: Add HCI capabilities sysfs group

On Sun, Aug 11, 2024 at 06:19:49AM +0000, Avri Altman wrote:
> > On Fri, Aug 09, 2024 at 10:23:31AM +0300, Avri Altman wrote:
> > > The standard register map of UFSHCI is comprised of several groups.
> > > The first group (starting from offset 0x00), is the host capabilities group.
> > > It contains some interesting information, that otherwise is not
> > > available, e.g. the UFS version of the platform etc.
> > >
> > > Reviewed-by: Keoseong Park <keosung.park@...sung.com>
> > > Reviewed-by: Bart Van Assche <bvanassche@....org>
> > > Signed-off-by: Avri Altman <avri.altman@....com>
> > > ---
> > >  Documentation/ABI/testing/sysfs-driver-ufs | 42 ++++++++++
> > >  drivers/ufs/core/ufs-sysfs.c               | 95 ++++++++++++++++++++++
> > >  2 files changed, 137 insertions(+)
> > >
> > > diff --git a/Documentation/ABI/testing/sysfs-driver-ufs
> > > b/Documentation/ABI/testing/sysfs-driver-ufs
> > > index fe943ce76c60..b6e0c3b806fd 100644
> > > --- a/Documentation/ABI/testing/sysfs-driver-ufs
> > > +++ b/Documentation/ABI/testing/sysfs-driver-ufs
> > > @@ -1532,3 +1532,45 @@ Contact:       Bean Huo <beanhuo@...ron.com>
> > >  Description:
> > >               rtc_update_ms indicates how often the host should synchronize or
> > update the
> > >               UFS RTC. If set to 0, this will disable UFS RTC periodic update.
> > > +
> > > +What:                /sys/devices/platform/.../ufshci_capabilities/capabilities
> > > +Date:                August 2024
> > > +Contact:     Avri Altman <avri.altman@....com>
> > > +Description:
> > > +             Host Capabilities register group: host controller capabilities register.
> > > +             Symbol - CAP.  Offset: 0x00 - 0x03.
> > 
> > This doesn't look like an ABI description. You are merely specifying the register
> > name and offset that gets accessed while reading this attribute.
> > 
> > Also, I'm not sure if we really want to expose HCI/MCQ capabilities as sysfs ABI.
> Why not?

sysfs is an userspace ABI. The information that is exposed is supposed to be
consumed by the sysadmins/userspace applications.

Looking at the contents of the capabilities, I don't think anyone could
interpret what is being exposed unless they have access to the spec (which is
not free).

> Like the cover letter say, this info is otherwise unavailable.

There are other ways to expose this information too, like debugfs. But what
exactly do you want users to do with it?

- Mani

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