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

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Message-ID: <56CD4BE1.3010701@ti.com>
Date:	Wed, 24 Feb 2016 11:51:21 +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 Tuesday 23 February 2016 11:58 PM, Paul Walmsley wrote:
> Kishon
> 
> On Tue, 23 Feb 2016, Kishon Vijay Abraham I wrote:
> 
>> On Monday 22 February 2016 03:25 PM, Kishon Vijay Abraham I wrote:
>>> On Monday 22 February 2016 12:01 PM, Paul Walmsley wrote:
>>>> On Mon, 22 Feb 2016, Kishon Vijay Abraham I wrote:
>>>>> On Thursday 18 February 2016 07:51 PM, Sekhar Nori wrote:
>>>>>> On Friday 12 February 2016 10:50 PM, Suman Anna wrote:
>>>>>>> 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.
>>
>> Do you expect any other testing from me?
> 
> No I think that's sufficient for the time being, thanks - but, two 
> questions:
> 
> 1. Can I add your Tested-by: ?

sure..
Tested-by: Kishon Vijay Abraham I <kishon@...com>

> 
> 2. Are you going to follow up with these PCIe core issues with the PCIe 
> core developers?

yeah, I see efforts have already started to convert the PCI drivers from
built-in to module [1] and issues arising out of that will be debugged.

Thanks
Kishon

[1] -> http://lkml.iu.edu/hypermail/linux/kernel/1602.0/06011.html
> 
> 
> - Paul
>