Re: [GIT PULL] FPGA Manager changes for 6.6-final

From: Greg KH <gregkh@linuxfoundation.org>
To: Marco Pagani <marpagan@redhat.com>
Cc: Xu Yilun <yilun.xu@linux.intel.com>,
	yilun.xu@intel.com, linux-fpga@vger.kernel.org, hao.wu@intel.com,
	mdf@kernel.org
Subject: Re: [GIT PULL] FPGA Manager changes for 6.6-final
Date: Wed, 18 Oct 2023 20:28:32 +0200	[thread overview]
Message-ID: <2023101857-surgical-gab-8469@gregkh> (raw)
In-Reply-To: <727498ba-8ea8-43b9-847b-0280a2bf94e3@redhat.com>

On Wed, Oct 18, 2023 at 05:40:08PM +0200, Marco Pagani wrote:
> On 2023-10-18 13:50, Greg KH wrote:
> > On Wed, Oct 18, 2023 at 11:39:01AM +0200, Marco Pagani wrote:
> >> On 18/10/23 09:50, Greg KH wrote:
> >>> On Wed, Oct 18, 2023 at 10:02:08AM +0800, Xu Yilun wrote:
> >>>> On Tue, Oct 17, 2023 at 07:17:29PM +0200, Greg KH wrote:
> >>>> NULL ptr is referenced.
> >>>>
> >>>> So do fpga-bridge/region-test.
> >>>>
> >>>> Patch #1 adds a common helper to generate a platform driver.
> >>>
> >>> Don't abuse platform devices/drivers like this, this is not a platform
> >>> device or driver.  If you really want to do this, use a real driver and
> >>> device, not a platform one please.
> >>
> >> Other test suites, like DRM suites, already use fake platform devices and
> >> drivers. Moreover, many real FPGA IPs, like reconfiguration controllers and
> >> bridges, are indeed modeled as platform devices. What is the benefit of
> >> using a real driver and device?
> > 
> > Again, please do not abuse platform devices and drivers when they should
> > not be used.  I can't catch all abuses, but when I do see them, I do
> > object to them.
> 
> Could you please elaborate a little more on why using platform drivers
> and devices for test cases is an abuse so I can improve the test suite?

Because they just are not platform devices.

A platform driver is one that has hardware resources like DT or ACPI or
other real resources that talk to hardware and are not on a discoverable
bus, they are NOT fake devices with no actual hardware resources.

If you need a "fake" device, make a fake device, that's what virtual
devices are for there are other solutions as well depending on how you
want to use it.

thanks,

greg k-h