Re: [PATCH 1/2] rtc: v3020: Add documentation for DT bindings

On Fri, Aug 25, 2017 at 5:36 PM, Brandon Martin [off-list ref] wrote:

On 08/25/2017 05:54 PM, Rob Herring wrote:

quoted

quoted

+
+Required for MMIO connection:
+  - reg : should contain registers location and length.

Looking at the datasheet, there's really no such thing. You'd have to
have some specialized h/w to generate the serial waveform.

If it's MMIO attached i.e. hooked up to a single data bit on an otherwise
multi-drop, flat addressed external bus, you do have to specify the memory
address at which one would access the device.  Length is irrelevant, yes, as
it has but one externally-accessible "register" in its memory map.

Is there a better way to handle this sort of thing than the typical "reg"
binding?  It certainly seems to map nicely to ioremap().

Okay, I guess you should keep that.

quoted

quoted

+
+Required for GPIO connection:
+- emmicro,use-gpio
+- cs-gpios, wr-gpios, rd-gpios, io-gpios : specify gpios connected to
+  corresponding pins of the RTC
+
+Optional properties:
+- emmicro,mmio-left-shift : data bit to which IO line is connected for
MMIO
+  connection (defaults to 0)

This has come up several times on RTCs (LP8841, DS1302). This really
looks like SPI and could probably use the spi-gpio bitbang driver.

Indeed it is perhaps like that.

This was a comparatively blind pass at DT-izing the existing driver without
other changes.  It does work and has immediate application on a mainline'd
DT board: Compulab CM-T3517 which is in fact what I'm porting to.

I don't think you could use spi-gpio bitbang if you had it memory-mapped,
and there are actual platforms that do this.  Some of Compulab's older PXA
based boards appear to do it, and they are in fact the boards still using
pdata rather than DT that caused me to keep that around when doing this.

I only meant for the GPIO based connection, that it looks like SPI bitbanging.

Rob
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