[PATCH 1/2] arm64: dts: qcom: sc7180: Switch SPI to use GPIO for CS

[Douglas Anderson <dianders@chromium.org>]

The geni SPI protocol appears to have been designed without taking
Linux needs into account.  In all the normal flows it takes care of
setting chip select itself.  However, Linux likes to manage the chip
select so it can do fancy things.

Back when we first landed the geni SPI driver we worked around this
by:
- Always setting the FRAGMENTATION bit in transfers, which (I believe)
  tells the SPI controller not to mess with the chip select during
  transfers.
- Controlling the chip select manually by sending the SPI controller
  commands to assert or deassert the chip select.

Our workaround was fine and it's been working OK, but it's really
quite inefficient.  A normal SPI transaction now needs to do:
1. Start a command to set the chip select.
2. Wait for an interrupt from controller saying chip select done.
3. Do a transfer.
4. Start a command to unset the chip select.
5. Wait for an interrupt from controller saying chip select done.

Things are made a bit worse because the Linux GPIO framework assumes
that setting a chip select is quick.  Thus the SPI core can be seen to
tell us to set our chip select even when it's already in the right
state and we were dutifully kicking off commands and waiting for
interrupts.  While we could optimize that particular case, we'd still
be left with the slowness when we actually needed to toggle the chip
select.

All the chip select lines can actually be muxed to be GPIOs and
there's really no downside in doing so.  Now Linux can assert and
deassert the chip select at will with a simple MMIO write.

The SPI driver will still have the ability to set the chip select, but
not we just won't use it.

With this change I tested reading the firmware off the EC connected to
a ChromeOS device (flashrom -p ec -r ...).  I saw about a 25% speedup
in total runtime of the command and a 30% reduction in interrupts
generated (measured by /proc/interrupts).

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 arch/arm64/boot/dts/qcom/sc7180.dtsi | 57 ++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/boot/dts/qcom/sc7180.dtsi b/arch/arm64/boot/dts/qcom/sc7180.dtsi
index 3a8076c8bdbf..74c8503b560e 100644
--- a/arch/arm64/boot/dts/qcom/sc7180.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180.dtsi
@@ -10,6 +10,7 @@
 #include <dt-bindings/clock/qcom,gpucc-sc7180.h>
 #include <dt-bindings/clock/qcom,rpmh.h>
 #include <dt-bindings/clock/qcom,videocc-sc7180.h>
+#include <dt-bindings/gpio/gpio.h>
 #include <dt-bindings/interconnect/qcom,sc7180.h>
 #include <dt-bindings/interrupt-controller/arm-gic.h>
 #include <dt-bindings/phy/phy-qcom-qusb2.h>
@@ -570,6 +571,7 @@ spi0: spi@880000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi0_default>;
 				interrupts = <GIC_SPI 601 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 37 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -607,6 +609,7 @@ spi1: spi@884000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi1_default>;
 				interrupts = <GIC_SPI 602 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 3 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -668,6 +671,7 @@ spi3: spi@88c000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi3_default>;
 				interrupts = <GIC_SPI 604 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 41 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -729,6 +733,7 @@ spi5: spi@894000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi5_default>;
 				interrupts = <GIC_SPI 606 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 28 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -779,6 +784,7 @@ spi6: spi@a80000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi6_default>;
 				interrupts = <GIC_SPI 353 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 62 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -840,6 +846,7 @@ spi8: spi@a88000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi8_default>;
 				interrupts = <GIC_SPI 355 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 45 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -901,6 +908,7 @@ spi10: spi@a90000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi10_default>;
 				interrupts = <GIC_SPI 357 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 89 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -938,6 +946,7 @@ spi11: spi@a94000 {
 				pinctrl-names = "default";
 				pinctrl-0 = <&qup_spi11_default>;
 				interrupts = <GIC_SPI 358 IRQ_TYPE_LEVEL_HIGH>;
+				cs-gpios = <&tlmm 56 GPIO_ACTIVE_LOW>;
 				#address-cells = <1>;
 				#size-cells = <0>;
 				status = "disabled";
@@ -1204,65 +1213,97 @@ pinmux {
 			qup_spi0_default: qup-spi0-default {
 				pinmux {
 					pins = "gpio34", "gpio35",
-					       "gpio36", "gpio37";
+					       "gpio36";
 					function = "qup00";
 				};
+				pinmux-cs {
+					pins = "gpio37";
+					function = "gpio";
+				};
 			};
 
 			qup_spi1_default: qup-spi1-default {
 				pinmux {
 					pins = "gpio0", "gpio1",
-					       "gpio2", "gpio3";
+					       "gpio2";
 					function = "qup01";
 				};
+				pinmux-cs {
+					pins = "gpio3";
+					function = "gpio";
+				};
 			};
 
 			qup_spi3_default: qup-spi3-default {
 				pinmux {
 					pins = "gpio38", "gpio39",
-					       "gpio40", "gpio41";
+					       "gpio40";
 					function = "qup03";
 				};
+				pinmux-cs {
+					pins = "gpio41";
+					function = "gpio";
+				};
 			};
 
 			qup_spi5_default: qup-spi5-default {
 				pinmux {
 					pins = "gpio25", "gpio26",
-					       "gpio27", "gpio28";
+					       "gpio27";
 					function = "qup05";
 				};
+				pinmux-cs {
+					pins = "gpio28";
+					function = "gpio";
+				};
 			};
 
 			qup_spi6_default: qup-spi6-default {
 				pinmux {
 					pins = "gpio59", "gpio60",
-					       "gpio61", "gpio62";
+					       "gpio61";
 					function = "qup10";
 				};
+				pinmux-cs {
+					pins = "gpio62";
+					function = "gpio";
+				};
 			};
 
 			qup_spi8_default: qup-spi8-default {
 				pinmux {
 					pins = "gpio42", "gpio43",
-					       "gpio44", "gpio45";
+					       "gpio44";
 					function = "qup12";
 				};
+				pinmux-cs {
+					pins = "gpio45";
+					function = "gpio";
+				};
 			};
 
 			qup_spi10_default: qup-spi10-default {
 				pinmux {
 					pins = "gpio86", "gpio87",
-					       "gpio88", "gpio89";
+					       "gpio88";
 					function = "qup14";
 				};
+				pinmux-cs {
+					pins = "gpio89";
+					function = "gpio";
+				};
 			};
 
 			qup_spi11_default: qup-spi11-default {
 				pinmux {
 					pins = "gpio53", "gpio54",
-					       "gpio55", "gpio56";
+					       "gpio55";
 					function = "qup15";
 				};
+				pinmux-cs {
+					pins = "gpio56";
+					function = "gpio";
+				};
 			};
 
 			qup_uart0_default: qup-uart0-default {
-- 
2.27.0.212.ge8ba1cc988-goog