@@ -1138,7 +1138,26 @@ clk_rcg2_shared_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
return clk_rcg2_recalc_rate(hw, parent_rate);
}
+static int clk_rcg2_shared_init(struct clk_hw *hw)
+{
+ struct clk_rcg2 *rcg = to_clk_rcg2(hw);
+
+ /* Initialize cached cfg so the parent is reported properly */
+ regmap_read(rcg->clkr.regmap, rcg->cmd_rcgr + CFG_REG, &rcg->parked_cfg);
+
+ /*
+ * Clear any force enable of the RCG from boot. We rely on child clks
+ * (branches) to turn the RCG on/off in the hardware and only set the
+ * enable bit in the RCG when we want to make sure the clk stays on for
+ * parent switches or parking.
+ */
+ clk_rcg2_clear_force_enable(hw);
+
+ return 0;
+}
+
const struct clk_ops clk_rcg2_shared_ops = {
+ .init = clk_rcg2_shared_init,
.enable = clk_rcg2_shared_enable,
.disable = clk_rcg2_shared_disable,
.get_parent = clk_rcg2_shared_get_parent,
There's two problems with shared RCGs. The first problem is that they incorrectly report the parent after commit 703db1f5da1e ("clk: qcom: rcg2: Cache CFG register updates for parked RCGs"). That's because the cached CFG register value needs to be populated when the clk is registered. clk_rcg2_shared_enable() writes the cached CFG register value 'parked_cfg'. This value is initially zero due to static initializers. If a driver calls clk_enable() first before setting a rate or parent, it will set the parent to '0' which is (almost?) always XO, and may not reflect the real parent. In the worst case, this switches the RCG from sourcing a fast PLL to the slow crystal speed. The second problem is that the force enable bit isn't cleared. The force enable bit is only used during parking and unparking of shared RCGs. Otherwise it shouldn't be set because it keeps the RCG enabled even when all the branches on the output of the RCG are disabled (the hardware has a feedback mechanism so that any child branches keep the RCG enabled when the branch enable bit is set). This problem wastes power if the clk is unused, and is harmful in the case that the clk framework disables the parent of the force enabled RCG. In the latter case, the GDSC the shared RCG is associated with will get wedged if the RCG's source clk is disabled and the GDSC tries to enable the RCG to do "housekeeping" while powering on. Both of these problems combined with incorrect runtime PM usage in the display driver lead to a black screen on Qualcomm sc7180 Trogdor chromebooks. What happens is that the bootloader leaves the 'disp_cc_mdss_rot_clk' enabled and the 'disp_cc_mdss_rot_clk_src' force enabled and parented to 'disp_cc_pll0'. The mdss driver probes and runtime suspends, disabling the mdss_gdsc which uses the 'disp_cc_mdss_rot_clk_src' for "housekeeping". The 'disp_cc_mdss_rot_clk' is disabled during late init because the clk is unused, but the parent 'disp_cc_mdss_rot_clk_src' is still force enabled because the force enable bit was never cleared. Then 'disp_cc_pll0' is disabled because it is also unused. That's because the clk framework believes the parent of the RCG is XO when it isn't. A child device of the mdss device (e.g. DSI) runtime resumes mdss which powers on the mdss_gdsc. This wedges the GDSC because 'disp_cc_mdss_rot_clk_src' is parented to 'disp_cc_pll0' and that PLL is off. With the GDSC wedged, mdss_runtime_resume() tries to enable 'disp_cc_mdss_mdp_clk' but it can't because the GDSC has wedged all the clks associated with the GDSC. disp_cc_mdss_mdp_clk status stuck at 'off' WARNING: CPU: 1 PID: 81 at drivers/clk/qcom/clk-branch.c:87 clk_branch_toggle+0x114/0x168 Modules linked in: CPU: 1 PID: 81 Comm: kworker/u16:4 Not tainted 6.7.0-g0dd3ee311255 #1 f5757d475795053fd2ad52247a070cd50dd046f2 Hardware name: Google Lazor (rev1 - 2) with LTE (DT) Workqueue: events_unbound deferred_probe_work_func pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : clk_branch_toggle+0x114/0x168 lr : clk_branch_toggle+0x110/0x168 sp : ffffffc08084b670 pmr_save: 00000060 x29: ffffffc08084b680 x28: ffffff808006de00 x27: 0000000000000001 x26: ffffff8080dbd4f4 x25: 0000000000000000 x24: 0000000000000000 x23: 0000000000000000 x22: ffffffd838461198 x21: ffffffd838007997 x20: ffffffd837541d5c x19: 0000000000000001 x18: 0000000000000004 x17: 0000000000000000 x16: 0000000000000010 x15: ffffffd837070fac x14: 0000000000000003 x13: 0000000000000004 x12: 0000000000000001 x11: c0000000ffffdfff x10: ffffffd838347aa0 x9 : 08dadf92e516c000 x8 : 08dadf92e516c000 x7 : 0000000000000000 x6 : 0000000000000027 x5 : ffffffd8385a61f2 x4 : 0000000000000000 x3 : ffffffc08084b398 x2 : ffffffc08084b3a0 x1 : 00000000ffffdfff x0 : 00000000fffffff0 Call trace: clk_branch_toggle+0x114/0x168 clk_branch2_enable+0x24/0x30 clk_core_enable+0x5c/0x1c8 clk_enable+0x38/0x58 clk_bulk_enable+0x40/0xb0 mdss_runtime_resume+0x68/0x258 pm_generic_runtime_resume+0x30/0x44 __genpd_runtime_resume+0x30/0x80 genpd_runtime_resume+0x124/0x214 __rpm_callback+0x7c/0x15c rpm_callback+0x30/0x88 rpm_resume+0x390/0x4d8 rpm_resume+0x43c/0x4d8 __pm_runtime_resume+0x54/0x98 __device_attach+0xe0/0x170 device_initial_probe+0x1c/0x28 bus_probe_device+0x48/0xa4 device_add+0x52c/0x6fc mipi_dsi_device_register_full+0x104/0x1a8 devm_mipi_dsi_device_register_full+0x28/0x78 ti_sn_bridge_probe+0x1dc/0x2bc auxiliary_bus_probe+0x4c/0x94 really_probe+0xf8/0x270 __driver_probe_device+0xa8/0x130 driver_probe_device+0x44/0x104 __device_attach_driver+0xa4/0xcc bus_for_each_drv+0x94/0xe8 __device_attach+0xf8/0x170 device_initial_probe+0x1c/0x28 bus_probe_device+0x48/0xa4 deferred_probe_work_func+0x9c/0xd8 process_scheduled_works+0x1ac/0x4dc worker_thread+0x110/0x320 kthread+0x100/0x120 ret_from_fork+0x10/0x20 Fixes: 703db1f5da1e ("clk: qcom: rcg2: Cache CFG register updates for parked RCGs") Reported-by: Stephen Boyd <sboyd@kernel.org> Closes: https://lore.kernel.org/r/1290a5a0f7f584fcce722eeb2a1fd898.sboyd@kernel.org Closes: https://issuetracker.google.com/319956935 Reported-by: Laura Nao <laura.nao@collabora.com> Closes: https://lore.kernel.org/r/20231218091806.7155-1-laura.nao@collabora.com Cc: Bjorn Andersson <andersson@kernel.org> Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> Cc: Douglas Anderson <dianders@chromium.org> Cc: Taniya Das <quic_tdas@quicinc.com> Signed-off-by: Stephen Boyd <swboyd@chromium.org> --- drivers/clk/qcom/clk-rcg2.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)