Re: [PATCH v5 00/14] Add BLK_CTL support for i.MX8MP

Abel Vesa
2021-03-04T00:26:46Z

On 20-11-03 13:18:12, Abel Vesa wrote:
> The BLK_CTL according to HW design is basically the wrapper of the entire
> function specific group of IPs and holds GPRs that usually cannot be placed
> into one specific IP from that group. Some of these GPRs are used to control
> some clocks, other some resets, others some very specific function that does
> not fit into clocks or resets. Since the clocks are registered using the i.MX
> clock subsystem API, the driver is placed into the clock subsystem, but it
> also registers the resets. For the other functionalities that other GPRs might
> have, the syscon is used.
>

This approach seems to be introducing a possible ABBA deadlock due to
the core clock and genpd locking. Here is a backtrace I got from Pete
Zhang (he reported the issue on the internal mailing list):

[ 11.667711][ T108] -> #1 (&genpd->mlock){+.+.}-{3:3}:
[ 11.675041][ T108] __lock_acquire+0xae4/0xef8
[ 11.680093][ T108] lock_acquire+0xfc/0x2f8
[ 11.684888][ T108] __mutex_lock+0x90/0x870
[ 11.689685][ T108] mutex_lock_nested+0x44/0x50
[ 11.694826][ T108] genpd_lock_mtx+0x18/0x24
[ 11.699706][ T108] genpd_runtime_resume+0x90/0x214 (hold genpd->mlock)
[ 11.705194][ T108] __rpm_callback+0x80/0x2c0
[ 11.710160][ T108] rpm_resume+0x468/0x650
[ 11.714866][ T108] __pm_runtime_resume+0x60/0x88
[ 11.720180][ T108] clk_pm_runtime_get+0x28/0x9c
[ 11.725410][ T108] clk_disable_unused_subtree+0x8c/0x144
[ 11.731420][ T108] clk_disable_unused_subtree+0x124/0x144
[ 11.737518][ T108] clk_disable_unused+0xa4/0x11c (hold prepare_lock)
[ 11.742833][ T108] do_one_initcall+0x98/0x178
[ 11.747888][ T108] do_initcall_level+0x9c/0xb8
[ 11.753028][ T108] do_initcalls+0x54/0x94
[ 11.757736][ T108] do_basic_setup+0x24/0x30
[ 11.762614][ T108] kernel_init_freeable+0x70/0xa4
[ 11.768014][ T108] kernel_init+0x14/0x18c
[ 11.772722][ T108] ret_from_fork+0x10/0x18

[ 11.777512][ T108] -> #0 (prepare_lock){+.+.}-{3:3}:
[ 11.784749][ T108] check_noncircular+0x134/0x13c
[ 11.790064][ T108] validate_chain+0x590/0x2a04
[ 11.795204][ T108] __lock_acquire+0xae4/0xef8
[ 11.800258][ T108] lock_acquire+0xfc/0x2f8
[ 11.805050][ T108] __mutex_lock+0x90/0x870
[ 11.809841][ T108] mutex_lock_nested+0x44/0x50
[ 11.814983][ T108] clk_unprepare+0x5c/0x100 ((hold prepare_lock))
[ 11.819864][ T108] imx8m_pd_power_off+0xac/0x110
[ 11.825179][ T108] genpd_power_off+0x1b4/0x2dc
[ 11.830318][ T108] genpd_power_off_work_fn+0x38/0x58 (hold genpd->mlock)
[ 11.835981][ T108] process_one_work+0x270/0x444
[ 11.841208][ T108] worker_thread+0x280/0x4e4
[ 11.846176][ T108] kthread+0x13c/0x14
[ 11.850621][ T108] ret_from_fork+0x10/0x18

Now, this has been reproduced only on the NXP internal tree, but I think
it is pretty obvious this could happen in upstream too, with this
patchset applied.

First, my thought was to change the prepare_lock/enable_lock in clock
core, from a global approach to a per clock basis. But that doesn't
actually fix the issue.

The usecase seen above is due to clk_disable_unused, but the same could
happen when a clock consumer calls prepare/unprepare on a clock.

I guess the conclusion is that the current state of the clock core and
genpd implementation does not support a usecase where a clock controller
has a PD which in turn uses another clock (from another clock controller).

Jacky, Pete, did I miss anything here ?

> Changes since v4:
> * added back the bus_blk_clk in the imx8mp blk_ctl driver (media_blk_ctl)
> * added the R-b tag from Rob to the documentation patch
>
> Abel Vesa (14):
> dt-bindings: clocks: imx8mp: Rename audiomix ids clocks to
> audio_blk_ctl
> dt-bindings: reset: imx8mp: Add audio blk_ctl reset IDs
> dt-bindings: clock: imx8mp: Add ids for the audio shared gate
> dt-bindings: clock: imx8mp: Add media blk_ctl clock IDs
> dt-bindings: reset: imx8mp: Add media blk_ctl reset IDs
> dt-bindings: clock: imx8mp: Add hdmi blk_ctl clock IDs
> dt-bindings: reset: imx8mp: Add hdmi blk_ctl reset IDs
> clk: imx8mp: Add audio shared gate
> Documentation: bindings: clk: Add bindings for i.MX BLK_CTL
> clk: imx: Add generic blk-ctl driver
> clk: imx: Add blk-ctl driver for i.MX8MP
> arm64: dts: imx8mp: Add audio_blk_ctl node
> arm64: dts: imx8mp: Add media_blk_ctl node
> arm64: dts: imx8mp: Add hdmi_blk_ctl node
>
> .../devicetree/bindings/clock/fsl,imx-blk-ctl.yaml | 60 ++++
> arch/arm64/boot/dts/freescale/imx8mp.dtsi | 37 +++
> drivers/clk/imx/Makefile | 2 +-
> drivers/clk/imx/clk-blk-ctl-imx8mp.c | 317 +++++++++++++++++++++
> drivers/clk/imx/clk-blk-ctl.c | 302 ++++++++++++++++++++
> drivers/clk/imx/clk-blk-ctl.h | 80 ++++++
> drivers/clk/imx/clk-imx8mp.c | 12 +-
> include/dt-bindings/clock/imx8mp-clock.h | 200 +++++++++----
> include/dt-bindings/reset/imx8mp-reset.h | 45 +++
> 9 files changed, 992 insertions(+), 63 deletions(-)
> create mode 100644 Documentation/devicetree/bindings/clock/fsl,imx-blk-ctl.yaml
> create mode 100644 drivers/clk/imx/clk-blk-ctl-imx8mp.c
> create mode 100644 drivers/clk/imx/clk-blk-ctl.c
> create mode 100644 drivers/clk/imx/clk-blk-ctl.h
>
> --
> 2.7.4
>