linux-kernel - Re: [PATCH 31/37] misc: Add host side pci driver for pci test function device

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Date:   Wed, 25 Jan 2017 11:10:53 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Arnd Bergmann <arnd@...db.de>, <linux-pci@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-samsung-soc@...r.kernel.org>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-arm-kernel@...s.com>,
        <linux-arm-msm@...r.kernel.org>, <nsekhar@...com>
Subject: Re: [PATCH 31/37] misc: Add host side pci driver for pci test
 function device

Hi,

On Tuesday 24 January 2017 09:32 PM, Christoph Hellwig wrote:
> On Thu, Jan 12, 2017 at 03:56:20PM +0530, Kishon Vijay Abraham I wrote:
>> Add PCI endpoint test driver that can verify base address
>> register, legacy interrupt/MSI interrupt and read/write/copy
>> buffers between host and device. The corresponding pci-epf-test
>> function driver should be used on the EP side.
> 
> Just curious:  what would you think of a text based (e.g. debugfs)
> interface to avoid the need for a userspace tool here?

I felt having a userspace tool gives the flexibility to add more tests
(iterations, sizes etc..) while the driver can just focus on performing simple
tests. Say we'd like to perform infinite read/write tests, it's better if the
userspace tool invokes read/write tests repeatedly instead of that being
implemented in the driver.
> 
>> +static const struct pci_device_id pci_endpoint_test_tbl[] = {
>> +	{ PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_ANY_ID) },
>> +	{ }
>> +};
>> +MODULE_DEVICE_TABLE(pci, pci_endpoint_test_tbl);
> 
> Also this looks really odd, and dangerous.  Probing for any
> TI device will bind to all kinds of legit devices.  It would
> be good if you could squeeze out a single id for this device

There is actually an id for the device, but I think we'll need an id for every
function right?

Having said that the id for the device is better than PCI_ANY_ID. Will fix it
in my next revision.

Thanks
Kishon