On Fri, Jun 15, 2018 at 11:17 AM, Sekhar Nori <nsekhar@xxxxxx> wrote: > Hi Rob, > > On Wednesday 13 June 2018 02:36 AM, Rob Herring wrote: >> On Tue, Jun 05, 2018 at 01:01:22AM -0500, Nishanth Menon wrote: >>> AM654 uses a UART controller that is compatible (partially) with >>> existing 8250 UART, however, has a few differences with respect to DMA >>> support and control paths. Introduce a base definition that allows us >>> to build up the differences in follow on patches. >>> >>> Cc: Sekhar Nori <nsekhar@xxxxxx> >>> Cc: Vignesh R <vigneshr@xxxxxx> >>> Signed-off-by: Nishanth Menon <nm@xxxxxx> >>> --- >>> Documentation/devicetree/bindings/serial/omap_serial.txt | 1 + >>> drivers/tty/serial/8250/8250_omap.c | 1 + >>> 2 files changed, 2 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/serial/omap_serial.txt b/Documentation/devicetree/bindings/serial/omap_serial.txt >>> index 4b0f05adb228..c35d5ece1156 100644 >>> --- a/Documentation/devicetree/bindings/serial/omap_serial.txt >>> +++ b/Documentation/devicetree/bindings/serial/omap_serial.txt >>> @@ -1,6 +1,7 @@ >>> OMAP UART controller >>> >>> Required properties: >>> +- compatible : should be "ti,am654-uart" for AM654 controllers >> >> Not compatible with any existing TI 8250 UARTs? > > Curious on why you asked about this. Are you suggesting why not: > > "ti,<new-soc>-uart", "ti,<old-soc>-uart" Correct. > or you are asking why introduce "ti,<new-soc>-uart" unless there is > clear demonstrable need for using it in driver code. > > In general, I think "ti,<new-soc>-uart", "ti,<old-soc>-uart" in > device-tree (and by extension in binding document) is better even in > there are no _known_ incompatibilities at the time of initial driver > submission. The reason is silicon integration and process differences > many times spill over into driver. Yes, and chip designers can't be trusted. ;) > Of course, the idea is not to go postal and create a new compatible for > every pin-compatible part number that gets created, but probably a new > compatible should be created for a new silicon die. Yes, that's the criteria I would use too. That's sometimes hard if it's not the chip vendor doing the DT bindings. > We have just started introducing support for this SoC, and since it > reuses many IPs, this question is likely to come up again. > > In this particular case though, Nishanth is perfectly right in not saying > > compatible : should be "ti,am654-uart", "ti,omap4-uart" > > Because we *know* UART DMA integration is different and a match against > omap4 would result in non-working UART once DMA is enabled by default. Okay, makes sense. I'd suggest rewording the commit message to include this. The "compatible to 8250 except for DMA" part I would have applied to all TI UARTs rather than DMA differences with other TI UARTs. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
