linux-kernel - Re: [PATCH v4 1/2] x86, pci: Reset PCIe devices at boot time

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Date:	Tue, 16 Oct 2012 20:45:50 +0900
From:	Takao Indoh <indou.takao@...fujitsu.com>
To:	khalid@...ehiking.org
CC:	linux-pci@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, martin.wilck@...fujitsu.com,
	kexec@...ts.infradead.org, hbabu@...ibm.com, andi@...stfloor.org,
	ddutile@...hat.com, ishii.hironobu@...fujitsu.com, hpa@...or.com,
	bhelgaas@...gle.com, tglx@...utronix.de, mingo@...hat.com,
	vgoyal@...hat.com
Subject: Re: [PATCH v4 1/2] x86, pci: Reset PCIe devices at boot time

(2012/10/16 2:17), Khalid Aziz wrote:
> On Mon, 2012-10-15 at 16:00 +0900, Takao Indoh wrote:
>> This patch resets PCIe devices at boot time by hot reset when
>> "reset_devices" is specified.
>>
>> Signed-off-by: Takao Indoh <indou.takao@...fujitsu.com>
>> ---
>>   arch/x86/include/asm/pci-direct.h |    1
>>   arch/x86/kernel/setup.c           |    3
>>   arch/x86/pci/early.c              |  344 ++++++++++++++++++++++++++++
>>   include/linux/pci.h               |    2
>>   init/main.c                       |    4
>>   5 files changed, 352 insertions(+), 2 deletions(-)
>>
>
>
> Looks good.
>
> Reviewed-by: Khalid Aziz <khalid@...ehiking.org>
>

Thanks! But unfortunately I found a bug, so I'll post v5 patch soon.

A bug I found is that configuration register is accessed without
delay after reset.

This is an algorithm to reset devices.

  for (each device) {  <===== (A)
    if (does not have downstream devices)
      continue
    for (each downstream device) {
      save config registers
    }
    do_bus_reset <==== (B)
  }
  wait 500 ms
  ...

Let's say my system has the following devices.

00:01.0 (root port)
|
+- 01:00.0 (device)

In this case,
1) At first, 00:01.0 is found at (A). And its downstream devcice 01:00.0
   is reset at (B).
2) Next, 01:00.0 is found at (A). Then config register of 01:00.0 is
   accessed. This is PCIe spec violation because the config register of
   01:00.0 is accessed without delay after reset. PCIe spec requires
   at least 100ms waiting time before sending a config request.

Therefore I'll update patches like this so that devices could be reset
after saving phase is done:

  for (each device) {
    if (does not have downstream devices)
      continue
    for_each (its downstream devices) {
      save config registers
    }
-   do_bus_reset
  }
+ for (each device) {
+   do_bus_reset
+ }
  wait 500 ms
  ...

Thanks,
Takao Indoh

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