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

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Date:   Mon, 21 Sep 2020 10:22:42 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        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

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
Kishon