From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: Re: [linux-sunxi] Re: [PATCH 4/5] ARM: dts: sun5i: Add dts file for the Empire Electronix D709 tablet Date: Tue, 22 Dec 2015 11:50:01 +0100 Message-ID: <56792AD9.9040209@redhat.com> References: <1450611782-9494-1-git-send-email-hdegoede@redhat.com> <1450611782-9494-4-git-send-email-hdegoede@redhat.com> <5677D87A.90805@redhat.com> <20151221161132.GA30359@lukather> <567854D5.7030601@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Chen-Yu Tsai Cc: Maxime Ripard , linux-arm-kernel , devicetree , linux-sunxi List-Id: devicetree@vger.kernel.org Hi, On 22-12-15 05:29, Chen-Yu Tsai wrote: > On Tue, Dec 22, 2015 at 3:36 AM, Hans de Goede wrote: >> Hi, >> >> On 21-12-15 17:11, Maxime Ripard wrote: >>> >>> Hi,x >>> >>> On Mon, Dec 21, 2015 at 11:46:18AM +0100, Hans de Goede wrote: >>>>> >>>>> On the side, any thoughts on how to handle the differences between >>>>> various "Q8" >>>>> tablets, like different I2C-based sensors and WiFi chips? >>>> >>>> >>>> For i2c based sensors the plan is to use devicetree overlays + an in >>>> kernel >>>> overlay manager which probes the i2c bus (checking known touchscreen / >>>> accelerometer >>>> addresses) and then picks the right touchscreen + accelerometer overlays. >>>> >>>> Wifi is somewhat more tricky I must admit, esp. since there seem to be q8 >>>> a23 based >>>> tablet variants with usb wifi and others with sdio wifi. Since both >>>> busses are >>>> discoverable I'm tempted to just enable both in devicetree, and let the >>>> kernel probe >>>> and see what is actually there. This assume that the way the wifichip is >>>> powered >>>> is the same on all boards, or at least that it is safe to enable the >>>> necessary >>>> regulators on all boards ... >>>> >>>>> I'm asking because with Maxime's couple-regulator we should be able to >>>>> get the >>>>> RTL8723BS on the Q8 A23/33 v1.5 working. >>>> >>>> >>>> So this means enabled the sdio controller (should be safe on all boards?) >>>> and >>>> enabling 2 regulators to power the wifi-chip. I think it will be safe to >>>> do this >>>> even on boards where those regulators are not used, what do you think ? >>> >>> >>> Wouldn't that introduce some useless power drain on those boards? >> >> >> If nothing is attached to those regulators (which I expect to be the case >> when >> they are not used to power wifi) then I would expect the drain to be >> minimal, >> my biggest worry is some board having tied these to ground, but I don't >> think >> that is very likely. > > AFAIK the AXP datasheets mention that unused DCDC outputs should be left > floating. Not sure if this applies to LDO outputs as well. But any used > outputs would have a bypass capacitor. > > From the board designs I've seen, this seems to be the common case. > I'm not an electrical engineer, but I think we're covered here. > > Another thing we need to deal with is the different power sequencing > requirements for the different SDIO chips. In my experience there are not that much sequences, as simply making sure all necessary resources are one before probing the sdio bus, I have yet to see a case where the order in which the resources are enabled matters. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html