From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Subject: Re: [PATCH 2/5] ARM: shmobile: r8a7791: add i2c master nodes to dtsi Date: Mon, 17 Feb 2014 10:11:37 +0100 Message-ID: References: <1392543658-5030-1-git-send-email-wsa@the-dreams.de> <1392543658-5030-3-git-send-email-wsa@the-dreams.de> <20140217075410.GA2633@katana> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: Sender: linux-sh-owner@vger.kernel.org To: Magnus Damm Cc: Wolfram Sang , SH-Linux , "linux-arm-kernel@lists.infradead.org" , "devicetree@vger.kernel.org" , Simon Horman List-Id: devicetree@vger.kernel.org On Mon, Feb 17, 2014 at 9:02 AM, Magnus Damm wrote: > On Mon, Feb 17, 2014 at 4:54 PM, Wolfram Sang wrote: >> On Sun, Feb 16, 2014 at 10:40:55AM +0100, Wolfram Sang wrote: >>> From: Wolfram Sang >>> >>> Signed-off-by: Wolfram Sang >> >> From your other mail: >> >> "[2/5] needs to be reworked to exclude the r8a7790 compatible string." >> >>> + compatible = "renesas,i2c-r8a7791", "renesas,i2c-r8a7790"; >> >> Why is that? From my knowledge, you start with the exact compatible >> property and hardware compatible entries may follow. Thanks for posting the link to the device tree wiki/quoting from it. I had faint memories of that quote, but couldn't remember where I read it. > I think this boils down to if they really are compatible or not. If > for instance a 16550 port would be compatible with 8250 on a hardware > level then using them in the order of "16550", "8250" makes sense. In > this case the r8a7791 i2c is not really strictly based on r8a7790 i2c, > it is just that r8a7790 has support in the driver. So it's a short cut > instead of actual hardware compatibility. > > So far we've dealt with this by updating the driver and only relying > on the actual SoC name as suffix. > > I'm sure there are tons of opinions. =) Hehe ;-) I think the tricky part is when a driver for "renesas,i2c-r8a7790" is updated with a new feature for r8a7790, which doesn't necessarily exist in r8a7791. Then the compatible entry above will cause breakage. In our case, this probably won't happen, as we will have "renesas,i2c-r8a7791" in the driver, but the driver could be forked in between the addition of "renesas,i2c-r8a7790" and "renesas,i2c-r8a7791" in our non-ideal world. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds