linux-kernel - RE: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4

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Date:   Fri, 4 Oct 2019 14:19:33 +0000
From:   <Mario.Limonciello@...l.com>
To:     <yehezkelshb@...il.com>, <mika.westerberg@...ux.intel.com>
CC:     <linux-usb@...r.kernel.org>, <andreas.noever@...il.com>,
        <michael.jamet@...el.com>, <rajmohan.mani@...el.com>,
        <nicholas.johnson-opensource@...look.com.au>, <lukas@...ner.de>,
        <gregkh@...uxfoundation.org>, <stern@...land.harvard.edu>,
        <anthony.wong@...onical.com>, <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4

> -----Original Message-----
> From: Limonciello, Mario
> Sent: Friday, October 4, 2019 9:06 AM
> To: 'Yehezkel Bernat'; Mika Westerberg
> Cc: linux-usb@...r.kernel.org; Andreas Noever; Michael Jamet; Rajmohan Mani;
> nicholas.johnson-opensource@...look.com.au; Lukas Wunner;
> gregkh@...uxfoundation.org; stern@...land.harvard.edu; Anthony Wong; LKML
> Subject: RE: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
> 
> >
> > On Fri, Oct 4, 2019 at 11:19 AM Mika Westerberg
> > <mika.westerberg@...ux.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.
> 

Sorry for the typo;  generation < 4.

> 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.
> 
> We would still of course read and analyze the NVM when it comes time to flash a
> new device
> though.