Hi,
On Thu, 9 Apr 2020 at 03:39, Mark Kettenis mark.kettenis@xs4all.nl wrote:
From: Andy Shevchenko andy.shevchenko@gmail.com Date: Thu, 9 Apr 2020 12:06:11 +0300
On Thu, Apr 9, 2020 at 2:00 AM Simon Glass sjg@chromium.org wrote:
At present if reading a BAR returns 0xffffffff (e.g. the device is not present) then the value is masked and a different value is returned. This makes it harder to detect the problem when debugging.
If you insisting on the code, you may need to reword the commit message, at least by removing ambiguous "device not present", because this is not how PCI spec defines situations when device is not present.
In addition to that:
The 0xffffffff value is an artifact of how x86 systems handle aborted PCI transactions. Other architectures will probably generate a fault of some sorts. It looks like at least some of the pci drivers in u-boot emulate the x86 behaviour but I'm not sure all of them do.
This is not intended to be used to detect missing devices. It's just that we should not be masking an obviously invalid value, to make it look more valid. It is very confusing.
I'll update the comment message.
Regards, Simon