linux-kernel - Re: [PATCH] block: mtip32xx: remove HOTPLUG_PCI

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Message-ID: <4F86228F.50705@micron.com>
Date:	Wed, 11 Apr 2012 17:32:15 -0700
From:	Asai Thambi S P <asamymuthupa@...ron.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Jens Axboe <axboe@...nel.dk>, Sam Bradshaw <sbradshaw@...ron.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: mtip32xx: remove HOTPLUG_PCI_PCIE dependancy

On 4/11/2012 3:37 PM, Greg KH wrote:

> On Wed, Apr 11, 2012 at 03:22:56PM -0700, Asai Thambi S P wrote:
>> On 4/11/2012 1:40 PM, Greg KH wrote:
>>
>>> On Wed, Apr 11, 2012 at 01:33:39PM -0700, Asai Thambi S P wrote:
>>>> On 4/11/2012 12:57 PM, Jens Axboe wrote:
>>>>
>>>>> On 2012-04-11 20:34, Greg KH wrote:
>>>>>> This removes the HOTPLUG_PCI_PCIE dependency on the driver and makes it
>>>>>> depend on PCI.
>>>>>
>>>>> I think it's an old dependency. I've built and run it here without as
>>>>> well, and no functional issues either.
>>>>>
>>>>> Sam/Asai?
>>>>>
>>>>
>>>>
>>>> Both driver and device will work fine without PCIe hotplug dependency. This
>>>> dependency is required for supporting surprise removal and surprise insertion
>>>> of the device on systems with PCIe hotplug controller.
>>>
>>> But that's not a driver-specific thing at all.  All PCI drivers need to
>>> be able to handle this (I like how you constantly check the pci id,
>>> that's cute.)
>>>
>>> So I think a basic dependancy on PCI should be fine here.
>>
>> The P320 is different from existing PCIe devices supporting surprise removal
>> and surprise insertion (SRSI) capability (aka hotplug). We equate the hotplug
>> functionality enabled by PCIe hotplug controllers to that of any other storage
>> endpoint (SAS, SATA, FC, etc). For those devices, hotplug functionality is
>> enabled by the transport layer and propagated up to host storage stack for
>> handling.
> 
> Huh?  No, hotplug on Linux happens on the PCI level, and has done so for
> over 10 years.

Just to clarify, I was referring to hotplug of SAS/SATA/FC storage devices,
not HBA.

> 
>> There are two types of users for P320 device – 1) those with systems that have
>> PCIe hotplug controllers and intend to use hotplug and 2) those who do not
>> need or intend to use hotplug. The HOTPLUG_PCI_PCIE dependency enables users
>> in the first bucket to use the device’s capability without affecting those in
>> the second bucket.
> 
> No, it prevents the users in the second group from ever using this
> driver as it will not be built at all.
> 
> I have such a system right here, and I want to use the device, yet could
> not as I do not have HOTPLUG_PCI_PCIE enabled in my kernel because I do
> not have that type of PCI Hotplug controller.
> 
>> While there aren’t many systems today that have PCIe
>> hotplug controllers, you will begin to see such systems very soon.
> 
> Manufacturers have been telling me that for over 10 years ago, when I
> got the first PCI Hotplug driver merged into the kernel tree :)
> 
>> The mtip32xx driver depends on remove() being called for graceful handling of
>> surprise removal events.
> 
> As it should, nothing new there, that's how PCI hotplug works.
> 
>> Such cleanup is necessary to enable clean surprise
>> insertion of the same/different device in the same slot. We do check the PCI
>> id in non-fast path code to detect the surprise removal and fail any
>> outstanding I/Os with -ENODEV, but the driver still depends on the pci core
>> with help from the pcie hotplug module to call remove() for cleanup, hence the
>> HOTPLUG_PCI_PCIE dependency.
> 
> No, that's not a valid dependency at all, sorry.
> 
> All you should depend on is CONFIG_PCI and CONFIG_BLOCK.  Your driver
> doesn't know, or care, if the system is a PCI hotplug one, as that is
> how we architected the PCI hotplug layer.  Otherwise all PCI drivers
> would have to have this type of logic in it, and that would be a lot of
> extra work for no good reason.
> 
> So, I still think this dependency should be removed, the fact that I'm
> typing this from a system running on this card at the moment, without
> PCIE hotplug capabilities, kind of proves it :)

Agree to remove the dependency. I will reply to Jens email too.

--
Regards,
Asai Thambi
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