Message-ID: <5864FF71.4080100@ti.com>
Date:   Thu, 29 Dec 2016 17:50:01 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Joao Pinto <Joao.Pinto@...opsys.com>,
        Bjorn Helgaas <helgaas@...nel.org>
CC:     Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <nsekhar@...com>, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] pci: rename *host* directory to *controller*

Hi,

On Thursday 29 December 2016 05:38 PM, Joao Pinto wrote:
> Às 11:58 AM de 12/29/2016, Kishon Vijay Abraham I escreveu:
>> Hi,
>>
>> On Thursday 29 December 2016 05:23 PM, Joao Pinto wrote:
>>> Às 11:48 AM de 12/29/2016, Kishon Vijay Abraham I escreveu:
>>>> Hi,
>>>>
>>>> On Thursday 29 December 2016 04:08 PM, Joao Pinto wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> Às 5:46 AM de 12/29/2016, Kishon Vijay Abraham I escreveu:
>>>>>> Hi,
>>>>>>
>>>>>> On Wednesday 28 December 2016 10:50 PM, Joao Pinto wrote:
>>>>>>> Às 5:17 PM de 12/28/2016, Joao Pinto escreveu:
>>>>>>>> Às 4:41 PM de 12/28/2016, Bjorn Helgaas escreveu:
>>>>>>>>> On Wed, Dec 28, 2016 at 01:57:13PM +0000, Joao Pinto wrote:
>>>>>>>>>> Às 9:22 AM de 12/28/2016, Christoph Hellwig escreveu:
>>>>>>>>>>> On Wed, Dec 28, 2016 at 01:39:37PM +0530, Kishon Vijay Abraham I wrote:
>>>>>>>>>>>> As discussed during our LPC discussions, I'm posting the rename patch
>>>>>>>>>>>> here. I'll post the rest of EP series before the next merge window.
>>>>>>>>>>>>
>>>>>>>>>>>> There might be hiccups because of this renaming but feel this is
>>>>>>>>>>>> necessary for long-term maintenance.
>>>>>>>>>>>
>>>>>>>>>>> if we do this rename it would be great to get it to Linus NOW after
>>>>>>>>>>> -rc1 as that minimizes the impact on the 4.11 merge window.
>>>>>>>>>>
>>>>>>>>>> Rename it to controller is a bit vague I thing since we have the PCI Endpoint IP
>>>>>>>>>> also. Wouldn't be better to name it rc_controller?
>>>>>>>>>
>>>>>>>>> I think Kishon's whole goal is to add PCI Endpoint IP, so he wants a
>>>>>>>>> neutral name that can cover both RC and Endpoint.
>>>>>>
>>>>>> right.
>>>>>>>>>
>>>>>>>>> I'm not a huge fan of "controller" because it feels a little bit long
>>>>>>>>> and while I suppose it technically does include the concept of the PCI
>>>>>>>>> interface of an endpoint, it still suggests more of the host side to
>>>>>>>>> me.
>>>>>>>>>
>>>>>>>>> Doesn't USB have a similar situation?  I see there's a
>>>>>>>>> drivers/usb/host/ (probably where we copied from in the first place).
>>>>>>>>> Is a USB gadget the USB analog of what you're doing?  How do they
>>>>>>>>> share code between the master/slave sides?
>>>>>>>>>
>>>>>>>>
>>>>>>>> The usb/host contains the implemnentations by the spec of the several
>>>>>>>> *hci (USB Host) and then you can have for example the USB 3.0 Designware
>>>>>>>> Host specific ops in dwc3 and for USB 2.0 in dwc2/.
>>>>>>
>>>>>> right, each IP have a separate directory in USB. I thought of doing something
>>>>>> similar for PCI but decided against it since that would involve identifying all
>>>>>> the PCI IPs used and eventually result in more directories.
>>>>>>>> For device purposes it uses the core/ and then some of the device functions
>>>>>>>> are extended from the gadget/ package in which you can use mass_storage and
>>>>>>>> other types of functions.
>>>>>>
>>>>>> That would be similar for PCI endpoint. All endpoint specific core
>>>>>> functionality will be added in drivers/pci/endpoint (see RFC [1]).
>>>>>>>>
>>>>>>>> In our case in PCI we have the core functions inside /drivers/pci and the host
>>>>>>>> mangled inside host. I suggest:
>>>>>>>>
>>>>>>>> drivers/pci
>>>>>>>>  drivers/pci/core/
>>>>>>>>  drivers/pci/core/hotplug
>>>>>>>>  drivers/pci/core/pcie
>>>>>>>>  drivers/pci/core/<all other files inside pci/ today>
>>>>>>>>  drivers/pci/host
>>>>>>>>  drivers/pci/dwc -> here would be pcie-designware and the specific vendor drivers
>>>>>>>
>>>>>>> Correction:
>>>>>>> drivers/pci/host/dwc -> here would be pcie-designware and the specific vendor
>>>>>>> drivers
>>>>>>>
>>>>>>>>  drivers/pci/<vendorN> -> here would be the drivers for vendorN controller
>>>>>>>
>>>>>>> Correction:
>>>>>>> drivers/pci/host/<vendorN> -> here would be the drivers for vendorN controller
>>>>>>>
>>>>>>>>  drivers/pci/endpoint -> common code
>>>>>>>>  drivers/pci/endpoint/dwc -> implementation of Synopsys specific endpoint ops
>>>>>>>>  drivers/pci/<vendorN> -> implementation of other vendors specific endpoint ops
>>>>>>
>>>>>> There are some parts of the dwc driver that is common to both root complex and
>>>>>> endpoint. Where should that be? I'm sure no one wants to duplicate the common
>>>>>> piece in both root complex and endpoint.
>>>>>
>>>>> You are right, the config space is almost the same and some ops also common.
>>>>> I would suggest:
>>>>>
>>>>> drivers/pci
>>>>>   drivers/pci/core/
>>>>>     drivers/pci/core/hotplug
>>>>>     drivers/pci/core/pcie
>>>>>     drivers/pci/core/<all other files inside pci/ today>
>>>>>   drivers/pci/dwc
>>>>>     drivers/pci/dwc/common.c -> common ops and registers between RC and endpoint
>>>>>     drivers/pci/dwc/host/
>>>>>     drivers/pci/dwc/endpoint/
>>>>>
>>>>> What do you think?
>>>>
>>>> I don't think we should have sub-directories within dwc (USB too doesn't have
>>>> sub-directories). Where should the platform specific driver be kept? For
>>>> example pci-dra7xx.c (which use dwc) has both rc and ep specific parts but the
>>>> changes are so minimal that splitting the file won't make much sense.
>>>>
>>>> And such a change would also mean we create a separate directory for every
>>>> other driver present right now in pci/host.
>>>
>>> I understand you idea. We can simplify it this way:
>>>
>>>  drivers/pci
>>>    drivers/pci/core/
>>>      drivers/pci/core/hotplug
>>>      drivers/pci/core/pcie
>>>      drivers/pci/core/<all other files inside pci/ today>
>>>      drivers/pci/dwc -> Common files (RC and EP), specific vendor drivers for EP
>>> and EP
>>>
>>> BTW dwc states for DesigWare Controller.
>>>
>>> What do you think?
>>
>> I'd like to avoid using different directory structures for different IPs. Lets
>> try to make it uniform.
> 
> I understand, but mixing them all up is not a good aproach in my opinion, since
> a SoCs using Synopsys IP will only use the common files for that IP. Today in
> the host/ folder you have a bunch of drivers that is not clear which are using
> Synopsys IP or not. Of course I mention Synopsys, because it is where I work,
> but the opinion would be the same for other IP vendor.

right, but it has been that way always. My point is why should we disturb it
for the sake of adding endpoint support.
> 
> I understand that you want to do a common Endpoint framework to be used by any
> IP vendor based, and maybe this partition makes it a bit harder, but in my
> personal opinion each IP vendor should have its own folder for clarity and
> organization of the code.
> 
> You framework should be outside those IP vendor folders and be available for
> their drivers to use it, and so it should be completely vendor agnostic.

right, that's how it was designed (please see drivers/pci/endpoint/ directories
in RFC [1] which has the endpoint framework).

[1] -> https://lkml.org/lkml/2016/9/14/27
> 
>>
>> Thanks
>> Kishon
>>
> 

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