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

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Date:   Fri, 4 Oct 2019 17:21:10 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario.Limonciello@...l.com
Cc:     yehezkelshb@...il.com, 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,
        christian@...lner.me
Subject: Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4

+Christian

On Fri, Oct 04, 2019 at 02:05:46PM +0000, Mario.Limonciello@...l.com wrote:
> > 
> > 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.
> 
> 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?