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

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Date:   Wed, 2 Oct 2019 11:34:46 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario.Limonciello@...l.com
Cc:     linux-usb@...r.kernel.org, andreas.noever@...il.com,
        michael.jamet@...el.com, YehezkelShB@...il.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

On Tue, Oct 01, 2019 at 05:05:09PM +0000, Mario.Limonciello@...l.com wrote:
> > @@ -322,9 +398,21 @@ static int tb_switch_nvm_add(struct tb_switch *sw)
> >  	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 != 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 purpose 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 !Intel but don't let
> it be written until ready to relax further.

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.