linux-kernel - Re: [PATCH v1 1/1] x86/PCI: Disable e820 usage for the resource allocation

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Message-ID: <Yqh3PtENhktETx4S@smile.fi.intel.com>
Date:   Tue, 14 Jun 2022 14:55:42 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ferry Toth <ftoth@...londelft.nl>
Subject: Re: [PATCH v1 1/1] x86/PCI: Disable e820 usage for the resource
 allocation

On Mon, Jun 13, 2022 at 05:35:20PM -0500, Bjorn Helgaas wrote:
> On Mon, Jun 13, 2022 at 11:16:41PM +0300, Andy Shevchenko wrote:
> > The resource management improve for PCI on x86 broke booting of Intel MID
> > platforms. It seems that the current code removes all available resources
> > from the list and none of the PCI device may be initialized. Restore the
> > old behaviour by force disabling the e820 usage for the resource allocation.
> > 
> > Fixes: 4c5e242d3e93 ("x86/PCI: Clip only host bridge windows for E820 regions")
> > Depends-on: fa6dae5d8208 ("x86/PCI: Add kernel cmdline options to use/ignore E820 reserved regions")
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> 
> Yeah, I blew it with 4c5e242d3e93.  Can you provide more details on
> how the MID platforms broke?

It's not so easy. The breakage seems affects the console driver and earlycon
doesn't work. erlyprintk doesn't support 32-bit MMIO addresses (again,
addresses, not data size). That said, there is nothing to show at all.

What I did, I have bisected to your patch, commented out the call and instead
added a printk() to see what it does, and it basically removed all resources
listed in _CRS.

> Since you set "pci_use_e820 = false" for
> MID below, I assume MID doesn't depend on the e820 clipping and thus
> should not break if we turn off clipping by default in 2023 as in
> 0ae084d5a674 ("x86/PCI: Disable E820 reserved region clipping starting
> in 2023").

> But it'd be nice to see the dmesg log and make sure.

Nothing to provide (see above why), sorry.

-- 
With Best Regards,
Andy Shevchenko