Re: [PATCH v9 01/23] clk: rk3568: Mark hclk_vo as critical

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On 2022-03-28 16:10, Sascha Hauer wrote:
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.

FWIW,

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
---

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 63dfbeeeb06d9..62694d95173ab 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 = {



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