The peric0_top1_ipclk_0 and peric0_top1_pclk_0 are the clocks going to
peric0/uart_usi, with pclk being the bus clock. Without pclk running,
any bus access will hang.
Unfortunately, in commit d97b6c902a40 ("arm64: dts: exynos: gs101:
update USI UART to use peric0 clocks") the gs101 DT ended up specifying
an incorrect pclk in the respective node and instead the two clocks
here were marked as critical.
As a side-effect and by accident, having them 'critical' also
worked-around a problem where earlycon stops to work sometime into the
boot for two reasons:
* peric0_top1_ipclk_0 requires its parent gout_cmu_peric0_ip to be
running, but because earlycon doesn't deal with clocks that
parent will be disabled when none of the other drivers that
actually deal with clocks correctly require it to be running and
the real serial driver (which does deal with clocks) hasn't taken
over yet
* hand-over between earlycon and serial driver appears to be
fragile and clocks get enabled and disabled a few times, which
also causes register access to hang while earlycon is still
active
(A wordier explanation can also be found in [1])
Since then, the DT has been updated to use the correct clock in
commit 21e4e8807bfc ("arm64: dts: exynos: gs101: use correct clocks for
usi_uart"). Furthermore, the clk core now helps OF platforms with their
stdout (earlycon) clocks during early boot and thereby avoids the
problem described above.
The driver here can now be corrected and the work-arounds removed. Do
so.
Link: https://lore.kernel.org/all/d45de3b2bb6b48653842cf1f74e58889ed6783ae.camel@xxxxxxxxxx/ [1]
Fixes: 893f133a040b ("clk: samsung: gs101: add support for cmu_peric0")
Signed-off-by: André Draszik <andre.draszik@xxxxxxxxxx>
Reviewed-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>
Reviewed-by: Sam Protsenko <semen.protsenko@xxxxxxxxxx>
---
v5: update commit message
v4:
- the earlycon issue described in the commit message in previous
versions of this patch is gone with "clk: samsung: gs101: allow
earlycon to work unconditionally", so no need to mention anything
v3:
- add git commit SHA1s (Krzysztof)
- add link to wordier description of earlycon issue
v2:
- commit message typo fixed
- collect Reviewed-by: tags
---
drivers/clk/samsung/clk-gs101.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/drivers/clk/samsung/clk-gs101.c b/drivers/clk/samsung/clk-gs101.c
index 85098c61c15e..9769c00b6ca8 100644
--- a/drivers/clk/samsung/clk-gs101.c
+++ b/drivers/clk/samsung/clk-gs101.c
@@ -3946,20 +3946,18 @@ static const struct samsung_gate_clock peric0_gate_clks[] __initconst = {
"gout_peric0_peric0_top0_pclk_9", "mout_peric0_bus_user",
CLK_CON_GAT_GOUT_BLK_PERIC0_UID_PERIC0_TOP0_IPCLKPORT_PCLK_9,
21, 0, 0),
- /* Disabling this clock makes the system hang. Mark the clock as critical. */
GATE(CLK_GOUT_PERIC0_PERIC0_TOP1_IPCLK_0,
"gout_peric0_peric0_top1_ipclk_0", "dout_peric0_usi0_uart",
CLK_CON_GAT_GOUT_BLK_PERIC0_UID_PERIC0_TOP1_IPCLKPORT_IPCLK_0,
- 21, CLK_IS_CRITICAL, 0),
+ 21, 0, 0),
GATE(CLK_GOUT_PERIC0_PERIC0_TOP1_IPCLK_2,
"gout_peric0_peric0_top1_ipclk_2", "dout_peric0_usi14_usi",
CLK_CON_GAT_GOUT_BLK_PERIC0_UID_PERIC0_TOP1_IPCLKPORT_IPCLK_2,
21, CLK_SET_RATE_PARENT, 0),
- /* Disabling this clock makes the system hang. Mark the clock as critical. */
GATE(CLK_GOUT_PERIC0_PERIC0_TOP1_PCLK_0,
"gout_peric0_peric0_top1_pclk_0", "mout_peric0_bus_user",
CLK_CON_GAT_GOUT_BLK_PERIC0_UID_PERIC0_TOP1_IPCLKPORT_PCLK_0,
- 21, CLK_IS_CRITICAL, 0),
+ 21, 0, 0),
GATE(CLK_GOUT_PERIC0_PERIC0_TOP1_PCLK_2,
"gout_peric0_peric0_top1_pclk_2", "mout_peric0_bus_user",
CLK_CON_GAT_GOUT_BLK_PERIC0_UID_PERIC0_TOP1_IPCLKPORT_PCLK_2,
--
2.46.0.rc2.264.g509ed76dc8-goog
