lkml.org 
[lkml]   [2018]   [Jun]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] PCI: shpchp: Fix probing logic inversion
From
Date
Bjorn, Mika,

On 25/06/18 15:01, Bjorn Helgaas wrote:
> Hi Marc,
>
> Sorry we broke this!

No worries, gave me a chance to stare at something else! ;-)

>
> On Thu, Jun 21, 2018 at 05:47:15PM +0100, Marc Zyngier wrote:
>> Until recently, shpc_probe() would bail out pretty early in the
>> absence of the SHPC capability. A logic change in the way the
>> driver now checks that capability makes it go and probe the
>> firmware anyway, with ugly consequences if the system is not
>> ACPI based (my arm64 ThunderX is DT driven, and explodes in
>> a spectacular way after getting a NULL root bridge from the
>> non-existent ACPI tables...).
>>
>> Take this opportunity to move the call to shpchp_is_native()
>> back into shpc_probe(), making it clear that a non-ACPI system
>> is not expected to use this driver.
>
> But a non-ACPI system *should* be able to use SHPC.

Yeah, I only realized that once Mika pointed it out.

> Here's my understanding of how it should work. On an ACPI system,
>
> - If firmware has _OSC, the OS calls it to request permission to
> manage the SHPC. If _OSC grants permission, it should also
> configure the hardware (interrupts, etc) to give the OS.
>
> - If there's no _OSC, shpchp assumes it's allowed to manage the
> SHPC, and it calls OSHP to configure the hardware appropriately.
>
> On a non-ACPI system, shpchp assumes there's no firmware involved at
> all, so it can manage the SHPC without doing anything special.
>
> I see Mika has already posted a patch similar to the first one
> below; I think either of those should fix the problem you're seeing.

Absolutely. With this early exit when root is NULL, my test box is back
up and running.

> The second is an attempt to clean things up so they make a
> little more sense.

I haven't tried that second patch yet, but from reading it, it
definitely helps making sense of this driver.

Thanks,

M.
--
Jazz is not dead. It just smells funny...

\
 
 \ /
  Last update: 2018-06-25 18:19    [W:0.057 / U:0.248 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site