linux-kernel - Re: [PATCH 1/3] mfd: cros_ec: Add Chrome OS EC userspace device interface

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Message-ID: <546DBC5B.803@collabora.co.uk>
Date:	Thu, 20 Nov 2014 11:03:07 +0100
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Olof Johansson <olof@...om.net>
CC:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Lee Jones <lee.jones@...aro.org>,
	Doug Anderson <dianders@...omium.org>,
	Bill Richardson <wfrichar@...omium.org>,
	Simon Glass <sjg@...gle.com>,
	Gwendal Grignou <gwendal@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mfd: cros_ec: Add Chrome OS EC userspace device interface

Hello Olof,

On 11/19/2014 09:45 PM, Olof Johansson wrote:
>> Is true that this is a new API for mainline but there is a lot of ChromeOS
>> installations that depends on this API which means that just replacing the
>> kernel with a mainline one there, will break existing user-space programs.
> 
> I think we can deal with that, at least if we pick new ioctl numbers
> so we can tell from the userspace tool which interface is in use
> during transition.
> 
>> But I understand that since those binaries were using a non-ustream kernel
>> it is expected that the kernel API could be changed.
>>
>> I think it would be great to keep existing binaries working but if changing
>> the API is required, then I can certainly do that when doing a re-spin.
> 
> I think there's some value in that, but i'm also somewhat embarrassed
> to have missed this aspect when doing internal review, and do agree
> with Alan. :) And we have only a few tools that use this interface so
> we should be able to cope with it.
> 
>

Thanks a lot for your feedback. I'll follow Alan suggestion then and make
the structs to be 64-bit safe and properly padded. Also, I'll follow your
suggestion and use a different magic number for the IOCTLs so user-space
programs can be backward compatible if needed.
 
> -Olof
> 

Best regards,
Javier
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