[PATCH v10 01/24] clk: rk3568: Mark hclk_vo as critical

[Sascha Hauer <s.hauer@pengutronix.de>]

Whenever pclk_vo is enabled hclk_vo must be enabled as well. This is
described in the Reference Manual as:

| 2.8.6 NIU Clock gating reliance
|
| A part of niu clocks have a dependence on another niu clock in order to
| sharing the internal bus. When these clocks are in use, another niu
| clock must be opened, and cannot be gated.  These clocks and the special
| clock on which they are relied are as following:
|
| Clocks which have dependency     The clock which can not be gated
| -----------------------------------------------------------------
| ...
| pclk_vo_niu, hclk_vo_s_niu       hclk_vo_niu
| ...

The clock framework doesn't offer a way to enable clock B whenever clock A is
enabled, at least not when B is not an ancestor of A. Workaround this by
marking hclk_vo as critical so it is never disabled. This is suboptimal in
terms of power consumption, but a stop gap solution until the clock framework
has a way to deal with this.

We have this clock tree:

|      aclk_vo                  2        2        0   300000000          0     0  50000         Y
|         aclk_hdcp             0        0        0   300000000          0     0  50000         N
|         pclk_vo               2        3        0    75000000          0     0  50000         Y
|            pclk_edp_ctrl      0        0        0    75000000          0     0  50000         N
|            pclk_dsitx_1       0        0        0    75000000          0     0  50000         N
|            pclk_dsitx_0       1        2        0    75000000          0     0  50000         Y
|            pclk_hdmi_host     1        2        0    75000000          0     0  50000         Y
|            pclk_hdcp          0        0        0    75000000          0     0  50000         N
|         hclk_vo               2        5        0   150000000          0     0  50000         Y
|            hclk_hdcp          0        0        0   150000000          0     0  50000         N
|            hclk_vop           0        2        0   150000000          0     0  50000         N

Without this patch the edp, dsitx, hdmi and hdcp driver would enable their
clocks which then enables pclk_vo, but hclk_vo stays disabled and register
accesses just hang. hclk_vo is enabled by the VOP2 driver, so reproducibility
of this issue depends on the probe order.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
---

Notes:
    Changes since v8:
    - new patch

 drivers/clk/rockchip/clk-rk3568.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/clk/rockchip/clk-rk3568.c b/drivers/clk/rockchip/clk-rk3568.c
index 606ae6cd918b2..f85902e2590c7 100644
--- a/drivers/clk/rockchip/clk-rk3568.c
+++ b/drivers/clk/rockchip/clk-rk3568.c
@@ -1591,6 +1591,7 @@ static const char *const rk3568_cru_critical_clocks[] __initconst = {
 	"hclk_php",
 	"pclk_php",
 	"hclk_usb",
+	"hclk_vo",
 };
 
 static const char *const rk3568_pmucru_critical_clocks[] __initconst = {
-- 
2.30.2