[PATCH v4 02/10] drivers: qcom: rpmh-rsc: Document the register layout better

[Douglas Anderson]

Perhaps it's just me, it took a really long time to understand what
the register layout of rpmh-rsc was just from the #defines.  Let's add
a bunch of comments describing which blocks are part of other blocks.

Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Reviewed-by: Maulik Shah <mkshah@xxxxxxxxxxxxxx>
---

Changes in v4: None
Changes in v3:
- Extra blank line removed (Maulik).
- IRQ registers aren't in TCS0 (Maulik).
- One space after a period now (Maulik).
- Plural of TCS fixed to TCSes following Maulik's example.
- Rebased atop v16 ('Invoke rpmh_flush...') series.

Changes in v2:
- Now prose in comments instead of struct definitions.
- Pretty ASCII art from Stephen.

 drivers/soc/qcom/rpmh-rsc.c | 79 ++++++++++++++++++++++++++++++++++---
 1 file changed, 74 insertions(+), 5 deletions(-)

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index 91fb5a6d68a2..439a0eadabf1 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -43,14 +43,29 @@
 #define DRV_NCPT_MASK			0x1F
 #define DRV_NCPT_SHIFT			27
 
-/* Register offsets */
+/* Offsets for common TCS Registers, one bit per TCS */
 #define RSC_DRV_IRQ_ENABLE		0x00
 #define RSC_DRV_IRQ_STATUS		0x04
-#define RSC_DRV_IRQ_CLEAR		0x08
-#define RSC_DRV_CMD_WAIT_FOR_CMPL	0x10
+#define RSC_DRV_IRQ_CLEAR		0x08	/* w/o; write 1 to clear */
+
+/*
+ * Offsets for per TCS Registers.
+ *
+ * TCSes start at 0x10 from tcs_base and are stored one after another.
+ * Multiply tcs_id by RSC_DRV_TCS_OFFSET to find a given TCS and add one
+ * of the below to find a register.
+ */
+#define RSC_DRV_CMD_WAIT_FOR_CMPL	0x10	/* 1 bit per command */
 #define RSC_DRV_CONTROL			0x14
-#define RSC_DRV_STATUS			0x18
-#define RSC_DRV_CMD_ENABLE		0x1C
+#define RSC_DRV_STATUS			0x18	/* zero if tcs is busy */
+#define RSC_DRV_CMD_ENABLE		0x1C	/* 1 bit per command */
+
+/*
+ * Offsets for per command in a TCS.
+ *
+ * Commands (up to 16) start at 0x30 in a TCS; multiply command index
+ * by RSC_DRV_CMD_OFFSET and add one of the below to find a register.
+ */
 #define RSC_DRV_CMD_MSGID		0x30
 #define RSC_DRV_CMD_ADDR		0x34
 #define RSC_DRV_CMD_DATA		0x38
@@ -67,6 +82,60 @@
 #define CMD_STATUS_ISSUED		BIT(8)
 #define CMD_STATUS_COMPL		BIT(16)
 
+/*
+ * Here's a high level overview of how all the registers in RPMH work
+ * together:
+ *
+ * - The main rpmh-rsc address is the base of a register space that can
+ *   be used to find overall configuration of the hardware
+ *   (DRV_PRNT_CHLD_CONFIG). Also found within the rpmh-rsc register
+ *   space are all the TCS blocks. The offset of the TCS blocks is
+ *   specified in the device tree by "qcom,tcs-offset" and used to
+ *   compute tcs_base.
+ * - TCS blocks come one after another. Type, count, and order are
+ *   specified by the device tree as "qcom,tcs-config".
+ * - Each TCS block has some registers, then space for up to 16 commands.
+ *   Note that though address space is reserved for 16 commands, fewer
+ *   might be present. See ncpt (num cmds per TCS).
+ *
+ * Here's a picture:
+ *
+ *  +---------------------------------------------------+
+ *  |RSC                                                |
+ *  | ctrl                                              |
+ *  |                                                   |
+ *  | Drvs:                                             |
+ *  | +-----------------------------------------------+ |
+ *  | |DRV0                                           | |
+ *  | | ctrl/config                                   | |
+ *  | | IRQ                                           | |
+ *  | |                                               | |
+ *  | | TCSes:                                        | |
+ *  | | +------------------------------------------+  | |
+ *  | | |TCS0  |  |  |  |  |  |  |  |  |  |  |  |  |  | |
+ *  | | | ctrl | 0| 1| 2| 3| 4| 5| .| .| .| .|14|15|  | |
+ *  | | |      |  |  |  |  |  |  |  |  |  |  |  |  |  | |
+ *  | | +------------------------------------------+  | |
+ *  | | +------------------------------------------+  | |
+ *  | | |TCS1  |  |  |  |  |  |  |  |  |  |  |  |  |  | |
+ *  | | | ctrl | 0| 1| 2| 3| 4| 5| .| .| .| .|14|15|  | |
+ *  | | |      |  |  |  |  |  |  |  |  |  |  |  |  |  | |
+ *  | | +------------------------------------------+  | |
+ *  | | +------------------------------------------+  | |
+ *  | | |TCS2  |  |  |  |  |  |  |  |  |  |  |  |  |  | |
+ *  | | | ctrl | 0| 1| 2| 3| 4| 5| .| .| .| .|14|15|  | |
+ *  | | |      |  |  |  |  |  |  |  |  |  |  |  |  |  | |
+ *  | | +------------------------------------------+  | |
+ *  | |                    ......                     | |
+ *  | +-----------------------------------------------+ |
+ *  | +-----------------------------------------------+ |
+ *  | |DRV1                                           | |
+ *  | | (same as DRV0)                                | |
+ *  | +-----------------------------------------------+ |
+ *  |                      ......                       |
+ *  +---------------------------------------------------+
+ */
+
 static u32 read_tcs_cmd(struct rsc_drv *drv, int reg, int tcs_id, int cmd_id)
 {
 	return readl_relaxed(drv->tcs_base + RSC_DRV_TCS_OFFSET * tcs_id + reg +
-- 
2.26.0.110.g2183baf09c-goog