linux-kernel - Re: [PATCH v3 3/3] pci: dra7xx: use pdata callbacks to perform reset

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Date:	Mon, 22 Feb 2016 15:25:47 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Paul Walmsley <paul@...an.com>
CC:	Sekhar Nori <nsekhar@...com>, Suman Anna <s-anna@...com>,
	<d-gerlach@...com>, Tony Lindgren <tony@...mide.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	<richardcochran@...il.com>, Russell King <linux@....linux.org.uk>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] pci: dra7xx: use pdata callbacks to perform reset

Hi Paul,

On Monday 22 February 2016 12:01 PM, Paul Walmsley wrote:
> Kishon,
> 
> On Mon, 22 Feb 2016, Kishon Vijay Abraham I wrote:
> 
>> Sekhar,
>>
>> On Thursday 18 February 2016 07:51 PM, Sekhar Nori wrote:
>>> On Friday 12 February 2016 10:50 PM, Suman Anna wrote:
>>>> Sekhar,
>>>> Will you be following up with above suggestion since Kishon is gonna be out?
>>>
>>> Alright, noticed this action for me :) Went through the thread, and 
>>> looks like this is what we want to see?
>>>
>>> Thanks,
>>> Sekhar
>>>
>>> ---8<---
>>> From e3ba368f2235e1bf38a22ba8ea4e5c12aaafda19 Mon Sep 17 00:00:00 2001
>>> Message-Id: <e3ba368f2235e1bf38a22ba8ea4e5c12aaafda19.1455803758.git.nsekhar@...com>
>>> From: Sekhar Nori <nsekhar@...com>
>>> Date: Thu, 18 Feb 2016 16:49:56 +0530
>>> Subject: [PATCH 1/1] ARM: DRA7: hwmod: Add custom reset handler for PCIeSS
>>>
>>> Add a custom reset handler for DRA7x PCIeSS. This
>>> handler is required to deassert PCIe hardreset lines
>>> after they have been asserted.
>>>
>>> This enables the PCIe driver to access registers after
>>> PCIeSS has been runtime enabled without having to
>>> deassert hardreset lines itself.
>>>
>>> With this patch applied, used lspci to make sure
>>> connected PCIe device enumerates on DRA74x and DRA72x
>>> EVMs.
>>>
>>> Signed-off-by: Sekhar Nori <nsekhar@...com>
>>> ---
>>> Applies to tag for-v4.6/omap-hwmod-a of Paul W's tree.
>>>
>>>  arch/arm/mach-omap2/omap_hwmod_7xx_data.c | 23 +++++++++++++++++++++++
>>>  1 file changed, 23 insertions(+)
>>>
>>> diff --git a/arch/arm/mach-omap2/omap_hwmod_7xx_data.c b/arch/arm/mach-omap2/omap_hwmod_7xx_data.c
>>> index b61355e2a771..252b74633e31 100644
>>> --- a/arch/arm/mach-omap2/omap_hwmod_7xx_data.c
>>> +++ b/arch/arm/mach-omap2/omap_hwmod_7xx_data.c
>>> @@ -1526,8 +1526,31 @@ static struct omap_hwmod dra7xx_ocp2scp3_hwmod = {
>>>   *
>>>   */
>>>  
>>> +/*
>>> + * As noted in documentation for _reset() in omap_hwmod.c, the stock reset
>>> + * functionality of OMAP HWMOD layer does not deassert the hardreset lines
>>> + * associated with an IP automatically leaving the driver to handle that
>>> + * by itself. This does not work for PCIeSS which needs the reset lines
>>> + * deasserted for the driver to start accessing registers.
>>> + *
>>> + * We use a PCIeSS HWMOD class specific reset handler to deassert the hardreset
>>> + * lines after asserting them.
>>> + */
>>> +static int dra7xx_pciess_reset(struct omap_hwmod *oh)
>>> +{
>>> +	int i;
>>> +
>>> +	for (i = 0; i < oh->rst_lines_cnt; i++) {
>>> +		omap_hwmod_assert_hardreset(oh, oh->rst_lines[i].name);
>>> +		omap_hwmod_deassert_hardreset(oh, oh->rst_lines[i].name);
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>> +
>>>  static struct omap_hwmod_class dra7xx_pciess_hwmod_class = {
>>>  	.name	= "pcie",
>>> +	.reset	= dra7xx_pciess_reset,
>>>  };
>>
>> Thanks for the patch.
> 
> Could you please test the bind/unbind functionality just to make sure it 
> works?

The pci-dra7xx driver neither expose the bind/unbind sysfs entry nor can be
built as module.

However I hacked the pci-dra7xx driver to be built as module [and reverted
Commit 5de85b9d57ab ("PM / runtime: Re-init runtime PM states at probe error
and driver unbind")] and I don't see an abort when the PCI registers are
accessed after rmmod/modprobe cycle (that was the issue that Sekhar's patch
tried to solve). However PCI as such doesn't work after rmmod/modprobe cycle
[1], but this is a different issue most likely in PCIe core and has to debugged.

In summary, there are other issues in PCI across rmmod/modprobe cycle but the
reset of pci-dra7xx happens fine with this patch.

Thanks
Kishon

[1] -> http://pastebin.ubuntu.com/15169387/