linux-kernel - Re: [RFC PATCH] fpga: Introduce new fpga subsystem

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Date:	Thu, 19 Sep 2013 12:03:39 +0200
From:	Pavel Machek <pavel@...x.de>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Jason Cooper <jason@...edaemon.net>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, monstr@...str.eu,
	Alan Tull <atull@...era.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dinh Nguyen <dinguyen@...era.com>,
	Philip Balister <philip@...ister.org>,
	Alessandro Rubini <rubini@...dd.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cesar Eduardo Barros <cesarb@...arb.net>,
	Joe Perches <joe@...ches.com>,
	"David S. Miller" <davem@...emloft.net>,
	Stephen Warren <swarren@...dia.com>,
	Arnd Bergmann <arnd@...db.de>,
	David Brown <davidb@...eaurora.org>,
	Dom Cobley <popcornmix@...il.com>
Subject: Re: [RFC PATCH] fpga: Introduce new fpga subsystem

Hi!

> > + Jason Gunthorpe
> 
> Thanks, looks interesting, we could possibly use this interface if it 
> met our needs..
>  
> > On Wed, Sep 18, 2013 at 05:56:39PM +0200, Michal Simek wrote:
> > > This new subsystem should unify all fpga drivers which
> > > do the same things. Load configuration data to fpga
> > > or another programmable logic through common interface.
> > > It doesn't matter if it is MMIO device, gpio bitbanging,
> > > etc. connection. The point is to have the same
> > > inteface for these drivers.
> 
> So, we have many years of in-field experience with this and this API
> doesn't really match what we do.
> 
> Here are the steps we perform, from userspace:
...

>  - Ask kernel to place FPGA into reset and prepare for programming
>    * Kernel can return an error (eg FPGA failed to erase, etc)
>    * this is the PROG_N low -> DONE high, PROG_N high -> INIT_N high
>      sequencing on Xilinx chips
>  - Ask kernel to load a bitstream.
>    * Userspace locats the bitstream file to load, and the mmaps it.
>    * Userspace passes the entire file in a single write() call to the
>      kernel which streams it over the configuration bus
>    * The kernel can report an erro rhere (eg Xilinx can report CRC
>    error)
>  - Ask the kernel to verify that configuration is complete. 
>    * On Xilinx this wait for done to go high
>  - Ask the kernel to release the configuration bus (tristate
>    all drivers) (or sometimes we have to drive the bus low,
>    it depends on the bitfile, user space knows what to do)
> 
> It is very important that userspace know exactly which step fails
> because the resolution is different. We use this in a manufacturing
> setting, so failures are expected and need quick root cause
> determination.
> 
> You could probably address that need by very clearly defining a
> variety of errno values for the various cases. However, it would be a
> disaster if every driver did something a little different :|

Well, exact steps are a bit hw-specific, too. So, if anything, I'd
suggest standartizing the errno values.

> Using request_firmware exclusively is not useful for us. We
> format the bitfile with a header that contains our internal tracking
> information. Sometimes we need to bitswap the bitfile. Our userspace
> handles all of this and can pass a bitfile in memory to write().

Take a look at
https://www.kernel.org/doc/Documentation/firmware_class/README . You
can do processing at 

 4), userspace:
     - hotplug: cat appropriate_firmware_image > \
       		    			       /sys/class/firmware/xxx/data

What is the specific reason request_firmware is unsuitable?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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