Re: [PATCH 2/6] crypto: jz4780-rng: Make ingenic CGU driver use syscon

Hi Paul,

Thanks for your review.

On 19 August 2017 at 02:18, Paul Burton [off-list ref] wrote:

Hi PrasannaKumar,

On Thursday, 17 August 2017 11:25:16 PDT PrasannaKumar Muralidharan wrote:

quoted

Ingenic PRNG registers are a part of the same hardware block as clock
and power stuff. It is handled by CGU driver. Ingenic M200 SoC has power
related registers that are after the PRNG registers. So instead of
shortening the register range use syscon interface to expose regmap.
This regmap is used by the PRNG driver.

Signed-off-by: PrasannaKumar Muralidharan <redacted>
---
 arch/mips/boot/dts/ingenic/jz4740.dtsi | 14 +++++++----
 arch/mips/boot/dts/ingenic/jz4780.dtsi | 14 +++++++----
 drivers/clk/ingenic/cgu.c              | 46
+++++++++++++++++++++------------- drivers/clk/ingenic/cgu.h              |
 9 +++++--
 drivers/clk/ingenic/jz4740-cgu.c       | 30 +++++++++++-----------
 drivers/clk/ingenic/jz4780-cgu.c       | 10 ++++----
 6 files changed, 73 insertions(+), 50 deletions(-)

diff --git a/arch/mips/boot/dts/ingenic/jz4740.dtsi

b/arch/mips/boot/dts/ingenic/jz4740.dtsi index 2ca7ce7..ada5e67 100644

--- a/arch/mips/boot/dts/ingenic/jz4740.dtsi
+++ b/arch/mips/boot/dts/ingenic/jz4740.dtsi

@@ -34,14 +34,18 @@
              clock-frequency = <32768>;
      };

-     cgu: jz4740-cgu@10000000 {
-             compatible = "ingenic,jz4740-cgu";
+     cgu_registers {
+             compatible = "simple-mfd", "syscon";
              reg = <0x10000000 0x100>;

-             clocks = <&ext>, <&rtc>;
-             clock-names = "ext", "rtc";
+             cgu: jz4780-cgu@10000000 {
+                     compatible = "ingenic,jz4740-cgu";

-             #clock-cells = <1>;
+                     clocks = <&ext>, <&rtc>;
+                     clock-names = "ext", "rtc";
+
+                     #clock-cells = <1>;
+             };
      };

      rtc_dev: rtc@10003000 {

diff --git a/arch/mips/boot/dts/ingenic/jz4780.dtsi

b/arch/mips/boot/dts/ingenic/jz4780.dtsi index 4853ef6..1301694 100644

--- a/arch/mips/boot/dts/ingenic/jz4780.dtsi
+++ b/arch/mips/boot/dts/ingenic/jz4780.dtsi

@@ -34,14 +34,18 @@
              clock-frequency = <32768>;
      };

-     cgu: jz4780-cgu@10000000 {
-             compatible = "ingenic,jz4780-cgu";
+     cgu_registers {
+             compatible = "simple-mfd", "syscon";
              reg = <0x10000000 0x100>;

-             clocks = <&ext>, <&rtc>;
-             clock-names = "ext", "rtc";
+             cgu: jz4780-cgu@10000000 {
+                     compatible = "ingenic,jz4780-cgu";

-             #clock-cells = <1>;
+                     clocks = <&ext>, <&rtc>;
+                     clock-names = "ext", "rtc";
+
+                     #clock-cells = <1>;
+             };
      };

      pinctrl: pin-controller@10010000 {

diff --git a/drivers/clk/ingenic/cgu.c b/drivers/clk/ingenic/cgu.c
index e8248f9..2f12c7c 100644
--- a/drivers/clk/ingenic/cgu.c
+++ b/drivers/clk/ingenic/cgu.c

@@ -29,6 +29,18 @@

 #define MHZ (1000 * 1000)

+unsigned int cgu_readl(struct ingenic_cgu *cgu, unsigned int reg)
+{
+     unsigned int val = 0;
+     regmap_read(cgu->regmap, reg, &val);
+     return val;
+}
+
+int cgu_writel(struct ingenic_cgu *cgu, unsigned int val, unsigned int reg)
+{
+     return regmap_write(cgu->regmap, reg, val);
+}

This is going to introduce a lot of overhead to the CGU driver - each
regmap_read() or regmap_write() call will not only add overhead from the
indirection but also acquire a lock which we really don't need.

Indeed.

Could you instead perhaps:

 - Just add "syscon" as a second compatible string to the CGU node in the
   device tree, but otherwise leave it as-is without the extra cgu_registers
   node.

 - Have your RNG device node as a child of the CGU node, which should let it
   pick up the regmap via syscon_node_to_regmap() as it already does.

 - Leave the CGU driver as-is, so it can continue accessing memory directly
   rather than via regmap.

As per my understanding, CGU driver and syscon will map the same
register set. Is that fine?

Thanks,
PrasannaKumar