net: dsa: sja1105: properly power down the microcontroller clock for SJA1110

It turns out that powering down the BASE_TIMER_CLK does not turn off the
microcontroller, just its timers, including the one for the watchdog.
So the embedded microcontroller is still running, and potentially still
doing things.

To prevent unwanted interference, we should power down the BASE_MCSS_CLK
as well (MCSS = microcontroller subsystem).

The trouble is that currently we turn off the BASE_TIMER_CLK for SJA1110
from the .clocking_setup() method, mostly because this is a Clock
Generation Unit (CGU) setting which was traditionally configured in that
method for SJA1105. But in SJA1105, the CGU was used for bringing up the
port clocks at the proper speeds, and in SJA1110 it's not (but rather
for initial configuration), so it's best that we rebrand the
sja1110_clocking_setup() method into what it really is - an implementation
of the .disable_microcontroller() method.

Since disabling the microcontroller only needs to be done once, at probe
time, we can choose the best place to do that as being in sja1105_setup(),
before we upload the static config to the device. This guarantees that
the static config being used by the switch afterwards is really ours.

Note that the procedure to upload a static config necessarily resets the
switch. This already did not reset the microcontroller, only the switch
core, so since the .disable_microcontroller() method is guaranteed to be
called by that point, if it's disabled, it remains disabled. Add a
comment to make that clear.

With the code movement for SJA1110 from .clocking_setup() to
.disable_microcontroller(), both methods are optional and are guarded by
"if" conditions.

Tested by enabling in the device tree the rev-mii switch port 0 that
goes towards the microcontroller, and flashing a firmware that would
have networking. Without this patch, the microcontroller can be pinged,
with this patch it cannot.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 3 deletions

diff --git a/drivers/net/dsa/sja1105/sja1105_clocking.c b/drivers/net/dsa/sja1105/sja1105_clocking.c
index 645edea5a81f..387a1f2f161c 100644
--- a/drivers/net/dsa/sja1105/sja1105_clocking.c
+++ b/drivers/net/dsa/sja1105/sja1105_clocking.c
@@ -6,6 +6,7 @@
 #include "sja1105.h"
 
 #define SJA1105_SIZE_CGU_CMD	4
+#define SJA1110_BASE_MCSS_CLK	SJA1110_CGU_ADDR(0x70)
 #define SJA1110_BASE_TIMER_CLK	SJA1110_CGU_ADDR(0x74)
 
 /* Common structure for CFG_PAD_MIIx_RX and CFG_PAD_MIIx_TX */
@@ -832,17 +833,30 @@ sja1110_cgu_outclk_packing(void *buf, struct sja1110_cgu_outclk *outclk,
 	sja1105_packing(buf, &outclk->pd,         0,  0, size, op);
 }
 
-/* Power down the BASE_TIMER_CLK in order to disable the watchdog */
-int sja1110_clocking_setup(struct sja1105_private *priv)
+int sja1110_disable_microcontroller(struct sja1105_private *priv)
 {
 	u8 packed_buf[SJA1105_SIZE_CGU_CMD] = {0};
+	struct sja1110_cgu_outclk outclk_6_c = {
+		.clksrc = 0x3,
+		.pd = true,
+	};
 	struct sja1110_cgu_outclk outclk_7_c = {
 		.clksrc = 0x5,
 		.pd = true,
 	};
+	int rc;
 
+	/* Power down the BASE_TIMER_CLK to disable the watchdog timer */
 	sja1110_cgu_outclk_packing(packed_buf, &outclk_7_c, PACK);
 
-	return sja1105_xfer_buf(priv, SPI_WRITE, SJA1110_BASE_TIMER_CLK,
+	rc = sja1105_xfer_buf(priv, SPI_WRITE, SJA1110_BASE_TIMER_CLK,
+			      packed_buf, SJA1105_SIZE_CGU_CMD);
+	if (rc)
+		return rc;
+
+	/* Power down the BASE_MCSS_CLOCK to gate the microcontroller off */
+	sja1110_cgu_outclk_packing(packed_buf, &outclk_6_c, PACK);
+
+	return sja1105_xfer_buf(priv, SPI_WRITE, SJA1110_BASE_MCSS_CLK,
 				packed_buf, SJA1105_SIZE_CGU_CMD);
 }