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Date:      Fri, 16 Nov 2018 10:45:39 +0530
From:      Rajesh Kumar <rajfbsd@gmail.com>
To:        freebsd-amd64@freebsd.org, freebsd-acpi@freebsd.org,  freebsd-hackers@freebsd.org
Subject:   Re: Enabling a ACPI eMMC device is causing kernel reboots with FreeBSD 11.2
Message-ID:  <CAAO%2BANPLyU7739hOYecbct_6X9P1OwyPPXPQOp9QKBMytS0H=g@mail.gmail.com>
In-Reply-To: <CAAO%2BANPD-K92dwUpQKWA%2BxTChbdxW8stXc=6mOq36zsGRk_5DA@mail.gmail.com>
References:  <CAAO%2BANPD-K92dwUpQKWA%2BxTChbdxW8stXc=6mOq36zsGRk_5DA@mail.gmail.com>

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Hi,

I did some study on this. During acpi_attach, if MCFG table is present,
FreeBSD tries to use it (That is to map the PCI Base address to virtual
address space).  Setting hw.pci.mcfg=0, disables that mapping and lets the
system use the type 1 config access (which is IO port based access).  So,
this is what hw.pci.mcfg does.

In our case, we are enabling a device on the ACPI bus and made sure no
other ACPI device collides with the address range for PCI (which mcfg
says). So, why enabling a device on ACPI, is causing the memory mapped PCI
access go bad to panic/reboot the kernel?  I tried to collect more info
enabling INVARIANTS, but in that case kernel panics much before in the boot
process. So, how could I proceed in debugging this issue? Any suggestions?


On Thu, Nov 8, 2018 at 4:14 PM Rajesh Kumar <rajfbsd@gmail.com> wrote:

> Hi,
>
> I have amd64 board, which has a eMMC device on the ACPI bus. When I try
> booting FreeBSD 11.2 on this board, with eMMC device disabled in BIOS, it
> boots without any issues.  But, when eMMC device is enabled in BIOS,
> FreeBSD 11.2 continuously reboots.
>
> When I have the following tunable set, FreeBSD 11.2 boots without any
> issues with eMMC enabled.
> hw.pci.mcfg=0
>
> Observations :
> a) We have verified the ACPI device addresses (from DSDT table) doesn't
> conflict with the PCI address base (configured in MCFG table).
> b) The PCI address base from MCFG table is read correctly by kernel
> (Verbose boot prints that address). So, I don't think MCFG table pointer is
> corrupted and getting read properly.
>
> Questions :
> a) What does hw.pci.mcfg=0 actually do to get the reboot issue resolved?
> b) Why enabling a device on ACPI bus needs hw.pci.mcfg (PCI specific) to
> boot?
>
> Looks like the system reboots when the ACPI and PCI devices enumeration
> starts during the boot. So, seems ACPI (or) PCI devices aren't getting
> enough resources and so reboots.
>
> Thanks,
> Rajesh.
>



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