linux-kernel - Re: [PATCH v5 14/17] NTB: Add support for EPF PCI-Express Non-Transparent Bridge

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Date:   Sun, 20 Sep 2020 21:58:16 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Kishon Vijay Abraham I <kishon@...com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Arnd Bergmann <arnd@...db.de>, Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <allenbh@...il.com>,
        Tom Joseph <tjoseph@...ence.com>, Rob Herring <robh@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-ntb@...glegroups.com
Subject: Re: [PATCH v5 14/17] NTB: Add support for EPF PCI-Express
 Non-Transparent Bridge

On 9/20/20 9:52 PM, Kishon Vijay Abraham I wrote:
> Hi Randy,
> 
> On 18/09/20 9:45 pm, Randy Dunlap wrote:
>> On 9/17/20 11:42 PM, Kishon Vijay Abraham I wrote:
>>> diff --git a/drivers/ntb/hw/epf/Kconfig b/drivers/ntb/hw/epf/Kconfig
>>> new file mode 100644
>>> index 000000000000..6197d1aab344
>>> --- /dev/null
>>> +++ b/drivers/ntb/hw/epf/Kconfig
>>> @@ -0,0 +1,6 @@
>>> +config NTB_EPF
>>> +	tristate "Generic EPF Non-Transparent Bridge support"
>>> +	depends on m
>>> +	help
>>> +	  This driver supports EPF NTB on configurable endpoint.
>>> +	  If unsure, say N.
>>
>> Hi,
>> Why is this driver restricted to 'm' (loadable module)?
>> I.e., it cannot be builtin.
> 
> I'm trying to keep all the host side PCI drivers corresponding to the
> devices configured using endpoint function drivers as modules and also
> not populate MODULE_DEVICE_TABLE() to prevent auto-loading.
> 
> The different endpoint function drivers (right now only pci-epf-test.c
> and pci-epf-ntb.c) can use the same device ID and vendorID for
> configuring the endpoint devices. So on the host side, it's possible an
> un-intended PCI driver can be bound to the device. So in-order to give
> users the flexibility of deciding the driver to be bound, I'm trying to
> keep it as modules. (Some driver like NTB also uses class code
> PCI_CLASS_MEMORY_RAM for binding a driver in addition to deviceID and
> vendorID but it need not be the case for all the drivers.)

Thanks for the explanation.

-- 
~Randy