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Date: Tue, 25 Jun 2013 16:27:37 +0200 From: Linus Walleij <linus.walleij@...aro.org> To: Stephen Warren <swarren@...dotorg.org> Cc: Christian Ruppert <christian.ruppert@...lis.com>, Patrice CHOTARD <patrice.chotard@...com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Grant Likely <grant.likely@...retlab.ca>, Rob Herring <rob.herring@...xeda.com>, Rob Landley <rob@...dley.net>, Sascha Leuenberger <sascha.leuenberger@...lis.com>, Pierrick Hascoet <pierrick.hascoet@...lis.com>, "devicetree-discuss@...ts.ozlabs.org" <devicetree-discuss@...ts.ozlabs.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, Alexandre Courbot <acourbot@...dia.com> Subject: Re: [PATCH 2/2] Make non-linear GPIO ranges accesible from gpiolib On Fri, Jun 21, 2013 at 11:17 PM, Stephen Warren <swarren@...dotorg.org> wrote: > When I pushed for the concept of groups, I intended it to mean precisely > one single thing. The points below describe this. > > 1) A pin is a single pin/ball/pad on the package. > > 2) Some register fields affect just a single pin. For example, there may > be a register field that affects pin A8's mux setting only. > > 3) Some register fields affect multiple pins at once. For example, > perhaps one register field affects both pin A8's an pin A7's mux setting > at once. > > 4) Depending on HW design, all register fields might be of type > described at (2) above, or all of the type described at (3) above, or a > mixture of both. Tegra is a mixture. > > 5) I expect the concept of a pin group to solely represent the various > groups of pins affected by each register field; in (2) above one pin per > group, in (3) above many pins per group. > > Thus, to my mind, a pin group is purely a HW concept, and dictated > purely by HW design. This we can discuss perpetually it seems. For Nomadik, as I've pointed out in the past it is actually: (6): it is one register/set if bits per pin, BUT the register settings pertain to physical lines having electrical settings which postulate that they be handled in batch or wreak havoc. I.e. it is a HW limitation in the *silicon* of *all* implementations, but that is *not* expressed in the register map. For the practical consequences see __nmk_config_pins if (glitch) runpath. Handling this as a group makes perfect sense from a hardware point of view. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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