linux-kernel - RE: Why does BIOS assign memory to 16 byte BAR

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Message-ID: <8520D5D51A55D047800579B094147198258BC67A@XAP-PVEXMBX01.xlnx.xilinx.com>
Date:	Wed, 27 Jul 2016 10:09:59 +0000
From:	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <helgaas@...nel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Arnd Bergmann <arnd@...db.de>, nofooter <nofooter@...inx.com>
Subject: RE: Why does BIOS assign memory to 16 byte BAR

> > We see that similar test is passing in x86 machine, where function one
> > requesting 1GB BAR's is failing, but function two requesting BAR's
> > with 16byte is getting assigned BAR's.
> >
> > To my knowledge on x86 BIOS assigns resources, or will kernel assign
> > reosurces on x86 ?  If kernel does is there any difference between x86
> > and arm64 resource assignment logic ?
>
> We can't answer your question if you do not provide a full log of x86 and
> ARM PCI configurations you are testing I am afraid.
>
> It is also unclear to me what "a similar test is passing in x86 machine" means,
> in particular in relation to the HW configuration you are testing on x86.
>
> Yes, there are differences between x86 and ARM resources assignments,
> x86 tries to claim PCI resources as set-up by BIOS and assign them iff the
> claiming fails whereas on ARM (and that's done in the host bridge driver) FW
> configuration is always discarded and the kernel reassigns the whole PCI
> resource hierarchy entirely, but to help we need more data as I said above.
>

Thanks Lorenzo.
I will try to get x86 configuration details soon and post, as the setup is at different location.
On ARM we using pcie-xilinx-nwl.c configurations where we have where we have 240MB BAR space
as per device tree documentation. (The kernel log I posted for testing purpose is using different address spaces,
if tests were successful, we will soon send patches for device tree)

Similar test case means, on x86 where we have multifunction device, where 1st function requests 1GB memory BAR's
and 2nd function requests 16byte memory BAR's, for 1st function BAR's are not assigned, but for 2nd function 16byte BAR assignment
is successful.

But on ARM similar test case fails to assign BAR's for both first function and second function.

What is the reason on ARM we are handling resource assignment in hierarchy format?
Because on ARM, in the above case due to lack of resources first function BAR assignment fails  which is fine but
even though we have enough resources for 16byte BAR allocations for second function, we are not assigning.

Thanks & Regards,
Bharat

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