linux-kernel - Re: [PATCH V2] ST SPEAr: PCIE gadget suppport

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Message-Id: <201101181551.47675.arnd@arndb.de>
Date:	Tue, 18 Jan 2011 15:51:47 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	pratyush <pratyush.anand@...com>
Cc:	Viresh KUMAR <viresh.kumar@...com>, Greg KH <greg@...ah.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Shiraz HASHIM <shiraz.hashim@...com>
Subject: Re: [PATCH V2] ST SPEAr: PCIE gadget suppport

On Monday 10 January 2011, pratyush wrote:

> >> +/*wait till link is up*/
> >> +# cat sys/devices/platform/pcie-gadget-spear.0/link
> >> +wait till it returns UP.
> > 
> > A blocking sysfs read is not a nice interface. This is probably where
> > the sysfs abstraction for your hardware stops making sense.
> > 
> 
> This call is not blocking. User will have to recheck link status till he
> finds it UP. He may put some delay between two successive read. I will
> modify documentation to be more explicit.

Ok, that is better, although with this interface you could argue that having
a blocking interface (not a sysfs file) would be useful to have.

> > The user interface for the interrupts looks to me like it should really
> > be based around a character device and either read/write/poll or
> > ioctl and poll. Using an eventfd might be cool here, because  then you
> > can combine this with other devices by passing the event file to
> > an interface that operates on eventfd. This would e.g. make it possible
> > to combine a UIO device generating interrupts with a PCIe gadget
> > sending the interrupts somewhere else, without leaving kernel
> > space.
> > 
> 
> I do not have much idea about eventfd mechanism. But if we decide to
> split it in two layers (generic pcie gadget and HW specific) then I
> might try to do it in this way.
 
ok.

	Arnd
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