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Re: Device probing and driver attach
On Fri, Nov 03, 2017 at 07:46:04PM +0100, Rocky Hotas wrote:
> - In principle, if one built a custom kernel including *only* the drivers
> needed by its current machine, would the boot time get significantly
Well, assuming any modernish bus with decent device enumeration
functionality, the answer is pretty much "it doesn't matter". Most of
the probe functions match things like bus/vendor IDs against a table.
There are very few PCI devices that are more involved like checking the
PCI config space (i.e. rtk vs re) and require many additional cycles. So
even with a thousand probe functions run with one microsecond teach, we
are talking about < 1 milli second per device. Given that the actual
hardware configuration often contains delay loops, probing simply doesn't
> - When a BIOS does not perform this operation, is during the
> autoconfiguration that device BARs are written by the OS?
There are two different parts here:
(1) Probing the size of a PCI BAR. This is done by the OS for general
(2) Reserving and/or assigning space for devices. This is generally
assumptions on x86 and many other platforms to be handled by the
firmware, with some fallback code i.e. for hot plugging bridges.
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