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From:   <Mario.Limonciello@dell.com>
To:     <mika.westerberg@linux.intel.com>
CC:     <linux-usb@vger.kernel.org>, <andreas.noever@gmail.com>,
        <michael.jamet@intel.com>, <YehezkelShB@gmail.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>
Subject: RE: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
Thread-Topic: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
Thread-Index: AQHVeEzShOhklesInk+gx9St4A7986dGAqiggAFZDQCAABiIsA==
Date:   Wed, 2 Oct 2019 15:04:33 +0000
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> -----Original Message-----
> From: Mika Westerberg <mika.westerberg@linux.intel.com>
> Sent: Wednesday, October 2, 2019 3:35 AM
> To: Limonciello, Mario
> Cc: linux-usb@vger.kernel.org; andreas.noever@gmail.com;
> michael.jamet@intel.com; YehezkelShB@gmail.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
> Subject: Re: [RFC PATCH 17/22] thunderbolt: Add initial support for USB4
>=20
>=20
> [EXTERNAL EMAIL]
>=20
> On Tue, Oct 01, 2019 at 05:05:09PM +0000, Mario.Limonciello@dell.com wrot=
e:
> > > @@ -322,9 +398,21 @@ static int tb_switch_nvm_add(struct tb_switch *s=
w)
> > >  	u32 val;
> > >  	int ret;
> > >
> > > -	if (!sw->dma_port)
> > > +	if (!nvm_readable(sw))
> > >  		return 0;
> > >
> > > +	/*
> > > +	 * The NVM format of non-Intel hardware is not known so
> > > +	 * currently restrict NVM upgrade for Intel hardware. We may
> > > +	 * relax this in the future when we learn other NVM formats.
> > > +	 */
> > > +	if (sw->config.vendor_id !=3D PCI_VENDOR_ID_INTEL) {
> > > +		dev_info(&sw->dev,
> > > +			 "NVM format of vendor %#x is not known, disabling
> NVM
> > > upgrade\n",
> > > +			 sw->config.vendor_id);
> > > +		return 0;
> > > +	}
> > > +
> >
> > Don't you actually have an attribute you can use here for this exact pu=
rpose
> that you
> > could  be setting rather than returning immediately?
> > sw->no_nvm_upgrade
> >
> > Then potentially you can at least let users "dump out" the nvm on !Inte=
l but
> don't let
> > it be written until ready to relax further.
>=20
> Problem is that we currently read NVM version and size from a known
> location in the NVM. If we don't know the format we can't do that so
> that would mean we need to expose active NVM with some size and hide
> nvm_version. I would rather have this support included in the kernel
> driver and expose standard set of attributes but no strong feelings from
> one way or another.

I agree with you; this is a safer and smarter approach to wait until detail=
s of format
for other vendors is known and export attributes only when it is.  This wil=
l also
encourage other vendors to open up their format if the only way to access N=
VM is
to document the headers.