linux-kernel - Re: [PATCH v1 3/7] PCI: New Primary to Sideband (P2SB) bridge support library

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Date:   Tue, 6 Apr 2021 15:40:01 +0200
From:   Henning Schild <henning.schild@...mens.com>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Jean Delvare <jdelvare@...e.de>,
        "Lee Jones" <lee.jones@...aro.org>,
        Tan Jui Nee <jui.nee.tan@...el.com>,
        "Jim Quinlan" <james.quinlan@...adcom.com>,
        Jonathan Yong <jonathan.yong@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-kernel@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, Jean Delvare <jdelvare@...e.com>,
        Peter Tyser <ptyser@...-inc.com>, <hdegoede@...hat.com>
Subject: Re: [PATCH v1 3/7] PCI: New Primary to Sideband (P2SB) bridge
 support library

Am Fri, 2 Apr 2021 15:09:12 +0200
schrieb "Enrico Weigelt, metux IT consult" <lkml@...ux.net>:

> On 09.03.21 09:42, Henning Schild wrote:
> 
> > The device will respond to MMIO while being hidden. I am afraid
> > nothing stops a collision, except for the assumption that the BIOS
> > is always right and PCI devices never get remapped. But just
> > guessing here.  
> 
> What could go wrong if it is remapped, except that this driver would
> write to the wrong mmio space ?
> 
> If it's unhidden, pci-core should see it and start the usual probing,
> right ?

I have seen this guy exposed to Linux on coreboot machines. No issues.
But i can imagine BIOSs that somehow make use of the device and assume
it wont move. So we would at least need a parameter to allow keeping
that device hidden, or "fixed" in memory.

Henning

> 
> --mtx
>