Re: [PATCH V4 2/4] arm64: dts: sc7280: Add QUPv3 wrapper_0 nodes

[Matthias Kaehlcke <mka@chromium.org>]

On Wed, Aug 11, 2021 at 05:43:48PM +0530, rajpat@codeaurora.org wrote:
> On 2021-07-26 21:32, Matthias Kaehlcke wrote:
> > On Mon, Jul 26, 2021 at 07:10:45PM +0530, Rajesh Patil wrote:
> > > From: Roja Rani Yarubandi <rojay@codeaurora.org>
> > > 
> > > Add QUPv3 wrapper_0 DT nodes for SC7280 SoC.
> > > 
> > > Signed-off-by: Roja Rani Yarubandi <rojay@codeaurora.org>
> > > Signed-off-by: Rajesh Patil <rajpat@codeaurora.org>
> > > ---
> > > Changes in V4:
> > >  - As per Bjorn's comment, added QUP Wrapper_0 nodes
> > >    other than debug-uart node
> > >  - Dropped interconnect votes for wrapper_0 node
> > > 
> > > Changes in V3:
> > >  - Broken the huge V2 patch into 3 smaller patches.
> > >    1. QSPI DT nodes
> > >    2. QUP wrapper_0 DT nodes
> > >    3. QUP wrapper_1 DT nodes
> > > 
> > > Changes in V2:
> > >  - As per Doug's comments removed pinmux/pinconf subnodes.
> > >  - As per Doug's comments split of SPI, UART nodes has been done.
> > >  - Moved QSPI node before aps_smmu as per the order.
> > > 
> > >  arch/arm64/boot/dts/qcom/sc7280-idp.dts |  84 ++++
> > >  arch/arm64/boot/dts/qcom/sc7280.dtsi    | 720
> > > ++++++++++++++++++++++++++++++++
> > >  2 files changed, 804 insertions(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/qcom/sc7280-idp.dts
> > > b/arch/arm64/boot/dts/qcom/sc7280-idp.dts
> > > index b0bfd8e..f63cf51 100644
> > > --- a/arch/arm64/boot/dts/qcom/sc7280-idp.dts
> > > +++ b/arch/arm64/boot/dts/qcom/sc7280-idp.dts
> > > @@ -358,6 +358,16 @@
> > >  	vdda18-supply = <&vreg_l1c_1p8>;
> > >  };
> > > 
> > > +&uart7 {
> > > +	status = "okay";
> > > +
> > > +	/delete-property/interrupts;
> > > +	interrupts-extended = <&intc GIC_SPI 608 IRQ_TYPE_LEVEL_HIGH>,
> > > +				<&tlmm 31 IRQ_TYPE_EDGE_FALLING>;
> > > +	pinctrl-names = "default", "sleep";
> > > +	pinctrl-1 = <&qup_uart7_sleep_cts>, <&qup_uart7_sleep_rts>,
> > > <&qup_uart7_sleep_tx>, <&qup_uart7_sleep_rx>;
> > > +};
> > > +
> > >  /* PINCTRL - additions to nodes defined in sc7280.dtsi */
> > > 
> > >  &qspi_cs0 {
> > > @@ -428,3 +438,77 @@
> > >  		bias-pull-up;
> > >  	};
> > >  };
> > > +&qup_uart7_cts {
> > > +	/*
> > > +	 * Configure a pull-down on CTS to match the pull of
> > > +	 * the Bluetooth module.
> > > +	 */
> > > +	bias-pull-down;
> > > +};
> > > +
> > > +&qup_uart7_rts {
> > > +	/* We'll drive RTS, so no pull */
> > > +	drive-strength = <2>;
> > > +	bias-disable;
> > > +};
> > > +
> > > +&qup_uart7_tx {
> > > +	/* We'll drive TX, so no pull */
> > > +	drive-strength = <2>;
> > > +	bias-disable;
> > > +};
> > > +
> > > +&qup_uart7_rx {
> > > +	/*
> > > +	 * Configure a pull-up on RX. This is needed to avoid
> > > +	 * garbage data when the TX pin of the Bluetooth module is
> > > +	 * in tri-state (module powered off or not driving the
> > > +	 * signal yet).
> > > +	 */
> > > +	bias-pull-up;
> > > +};
> > > +
> > > +&tlmm {
> > > +	qup_uart7_sleep_cts: qup-uart7-sleep-cts {
> > > +		pins = "gpio28";
> > > +		function = "gpio";
> > > +		/*
> > > +		 * Configure a pull-down on CTS to match the pull of
> > > +		 * the Bluetooth module.
> > > +		 */
> > > +		bias-pull-down;
> > > +	};
> > > +
> > > +	qup_uart7_sleep_rts: qup-uart7-sleep-rts {
> > > +		pins = "gpio29";
> > > +		function = "gpio";
> > > +		/*
> > > +		 * Configure pull-down on RTS. As RTS is active low
> > > +		 * signal, pull it low to indicate the BT SoC that it
> > > +		 * can wakeup the system anytime from suspend state by
> > > +		 * pulling RX low (by sending wakeup bytes).
> > > +		 */
> > > +		bias-pull-down;
> > > +	};
> > > +
> > > +	qup_uart7_sleep_tx: qup-uart7-sleep-tx {
> > > +		pins = "gpio30";
> > > +		function = "gpio";
> > > +		/*
> > > +		 * Configure pull-up on TX when it isn't actively driven
> > > +		 * to prevent BT SoC from receiving garbage during sleep.
> > > +		 */
> > > +		bias-pull-up;
> > > +	};
> > > 
> > > +	qup_uart7_sleep_rx: qup-uart7-sleep-rx {
> > > +		pins = "gpio31";
> > > +		function = "gpio";
> > > +		/*
> > > +		 * Configure a pull-up on RX. This is needed to avoid
> > > +		 * garbage data when the TX pin of the Bluetooth module
> > > +		 * is floating which may cause spurious wakeups.
> > > +		 */
> > > +		bias-pull-up;
> > > +	};
> > > +};
> > 
> > How the patches of this series are split strikes me as a bit odd.
> > Supposedly
> > this patch adds the QUPv3 wrapper_0 DT nodes for the SC7280, however the
> > above is the pin configuration for the Bluetooth UART of the SC7280 IDP
> > board.
> > I don't see a good reason why that should be part of this patch. It
> > should be
> > a separate change whose subject indicates that it configures the
> > Bluetooth UART
> > of the SC7280 IDP.
> > 
> 
> Okay will split this up.
> 
> > Without this conflation of SoC and board DT it would seem perfectly
> > reasonable
> > to squash this patch and '[4/4] arm64: dts: sc7280: Add QUPv3 wrapper_1
> > nodes'
> > into a single one, they are essentially doing the same thing, I see no
> > need to
> > have different patches for the wrapper 0 and 1 nodes.
> 
> Previously when QUP wrapper 0 and wrapper 1 nodes were added in single
> patch, we faced some git issues as the patch was huge. Hence we split it up.
> https://partnerissuetracker.corp.google.com/issues/177045897#comment12

That bug tracker entry isn't public, this is what the comment says:

> I suspect that diff is just having a hard time since your patch touches so
> much stuff. Presumably you could make it happier if you broke your patch
> into smaller changes. For instance:
> 
> One patch that adds the quad SPI. After all the quad SPI isn't really
> related to the other QUP stuff. One patch that fixes up the existing
> "uart5" and the QUP it's on to be how it's supposed to be. One patch
> that adds all the new stuff.

If I understand correctly the problem wasn't that the QUP wrappers are
added in a single patch (which should be pretty straightforward to
review), but that the previous patch(es) do too many things at once.
Adding both QUP wrappers is conceptionally a single thing, the problem
is intermingling that with adding board specific Bluetooth nodes, board
flash nodes, pinconf for UART, etc