Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4

From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Mario.Limonciello@dell.com
Cc: yehezkelshb@gmail.com, linux-usb@vger.kernel.org,
	andreas.noever@gmail.com, michael.jamet@intel.com,
	rajmohan.mani@intel.com,
	nicholas.johnson-opensource@outlook.com.au, lukas@wunner.de,
	gregkh@linuxfoundation.org, stern@rowland.harvard.edu,
	anthony.wong@canonical.com, linux-kernel@vger.kernel.org,
	christian@kellner.me
Subject: Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
Date: Fri, 4 Oct 2019 17:21:10 +0300	[thread overview]
Message-ID: <20191004142110.GJ2819@lahna.fi.intel.com> (raw)
In-Reply-To: <332849ed8714496587251b6319a11b0b@AUSX13MPC105.AMER.DELL.COM>

+Christian

On Fri, Oct 04, 2019 at 02:05:46PM +0000, Mario.Limonciello@dell.com wrote:
> > 
> > On Fri, Oct 4, 2019 at 11:19 AM Mika Westerberg
> > <mika.westerberg@linux.intel.com> wrote:
> > >
> > > On Fri, Oct 04, 2019 at 11:07:34AM +0300, Yehezkel Bernat wrote:
> > > > > Also if you can get the hw_vendor_id and hw_product_id from the kernel
> > > > > does that mean you don't need to do the two reads or you still need
> > > > > those?
> > > >
> > > > Are those the chip vendor or the OEM, in case they are different?
> > >
> > > Those are the actual USB4 hardware maker values, directly from
> > > ROUTER_CS_0 (p. 287 in the USB4 spec). This almost certainly differ from
> > > the OEM values from DROM we currently expose.
> > 
> > Makes sense to me. Userspace can learn the relevant IDs that their NVM format
> > is
> > known.
> > 
> > >
> > > > Thinking about it again, I'd guess it shouldn't matter much, if the chip is from
> > > > Intel, the FW supports NVM upgrade, isn't it?
> > >
> > > So the bottom line is that if the kernel thinks the router supports NVM
> > > upgrade it exposes the nvm_active/nvm_non_active files etc. I think
> > > fwupd uses this information to display user whether the device can be
> > > upgraded or not (for example ICL cannot as the NVM is part of BIOS).
> > 
> > Yes, fwupd already takes this into account, but the question here is how to
> > handle cases that NVM is available but the format isn't known to
> > userspace (yet).
> 
> Exactly.
> 
> > 
> > >
> > > Exposing hw_vendor_id and hw_product_id may speed up fwupd because it
> > > does not need to go over the active NVM to figure out whether the new
> > > image is for the correct controller.
> > 
> > It's not about finding the relevant image for upgrade (which must be searched
> > for by looking in the DROM vendor/product values), but about the question if the
> > NVM format is known to userspace and skip the parsing work if it's anyway going
> > to fail.
> > 
> > So yes, I think exposing vendor ID (and maybe also product ID) can improve the
> > situation.
> > 
> 
> Currently at probe time everything comes from udev except for the bit indicating
> running in "native" mode or not.  Just enough chunks of the NVM are read to determine
> that (IE no reading up through DROM or jumping around).
> 
> If Christian's patch to export generation is accepted I think that we could move that check
> to only read -native if generation < 3.
> 
> And if you export the hw_vendor_id and hw_product_id fields then that means USB4 devices
> would require no reading from NVM at "probe" since we don't have to read a -native bit.

Right. So I'm thinking instead of sw->generation what if we expose three
new attributes:

  hw_vendor_id - Hardware Vendor ID read from ROUTER_CS_0.
  hw_product_id - Hardware Product ID read from ROUTER_CS_0.
  hw_version - Hardware USB4 version read from ROUTER_CS_4.

This should allow userspace to determine what exactly the device is and
which version it is. For example USB4 routers the hw_version is 0x20.

@Christian, would this work for bolt as well?