Hi Stephen,
On Tue, 9 Jul 2024 at 00:03, Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote:
>
> Quoting Stephen Boyd (2024-05-02 15:47:02)
> > 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() before
> > setting a rate or parent, it will set the parent to '0' which is
> > (almost?) always XO, and may not reflect the parent at registration. 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
> > causing clks to stay stuck off.
> >
> > This leads to the following warning seen at boot and a black screen
> > because the display driver fails to probe.
> >
> > 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
> >
> > Fix these problems by parking shared RCGs at boot. This will properly
> > initialize the parked_cfg struct member so that the parent is reported
> > properly and ensure that the clk won't get stuck on or off because the
> > RCG is parented to the safe source (XO).
> >
> > Fixes: 703db1f5da1e ("clk: qcom: rcg2: Cache CFG register updates for parked RCGs")
> > Reported-by: Stephen Boyd <sboyd@xxxxxxxxxx>
> > Closes: https://lore.kernel.org/r/1290a5a0f7f584fcce722eeb2a1fd898.sboyd@xxxxxxxxxx
> > Closes: https://issuetracker.google.com/319956935
> > Reported-by: Laura Nao <laura.nao@xxxxxxxxxxxxx>
> > Closes: https://lore.kernel.org/r/20231218091806.7155-1-laura.nao@xxxxxxxxxxxxx
> > Cc: Bjorn Andersson <andersson@xxxxxxxxxx>
> > Cc: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > Cc: Douglas Anderson <dianders@xxxxxxxxxxxx>
> > Cc: Taniya Das <quic_tdas@xxxxxxxxxxx>
> > Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> > ---
>
> Applied to clk-next
>
This patch caused a few deferred probes on sm8550-hdk breaking the
audio codec and usb-c host mode support. This breakage is not 100%
reproducible but can be fairly easily reproduced though.
I have attached the relevant logs and defconfig here
https://bugs.linaro.org/show_bug.cgi?id=6053 for reference. Let me
know if you need more information or if I can assist you in testing a
debug patch to diagnose it further.
Regards,
Amit Pundir
