Re: [PATCH v9 2/3] PCI: Add tango PCIe host bridge support

From: Mason
Date: Tue Jul 04 2017 - 20:01:18 EST

On 03/07/2017 20:11, Russell King - ARM Linux wrote:

> I don't think there's an easy solution to this problem - and I'm not
> sure that stop_machine() can be made to work in this path (which
> needs a process context). I have a suspicion that the Sigma Designs
> PCI implementation is just soo insane that it's never going to work
> reliably in a multi-SoC kernel without introducing severe performance
> issues for everyone else.

If I remember correctly, this is the second HW block from
tango that has been deemed "too insane for Linux".

The first one was the DMA engine, which doesn't interrupt
when a transfer is done, but when a new transfer may be
programmed. (Though there is a simple work-around for
this one, if we give up command pipelining.)

Do larger SoC vendors have HW devs working closely with
Linux devs, to avoid these design bloopers?