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

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Date:   Tue, 1 Oct 2019 17:05:09 +0000
From:   <Mario.Limonciello@...l.com>
To:     <mika.westerberg@...ux.intel.com>, <linux-usb@...r.kernel.org>
CC:     <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

> @@ -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.

>  	nvm = kzalloc(sizeof(*nvm), GFP_KERNEL);
>  	if (!nvm)
>  		return -ENOMEM;