From: Doug Anderson <dianders@chromium.org>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@kernel.org>,
Bjorn Andersson <andersson@kernel.org>,
linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org,
patches@lists.linux.dev, linux-arm-msm@vger.kernel.org,
Laura Nao <laura.nao@collabora.com>,
Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
Taniya Das <quic_tdas@quicinc.com>
Subject: Re: [PATCH] clk: qcom: Park shared RCGs upon registration
Date: Thu, 2 May 2024 16:20:31 -0700 [thread overview]
Message-ID: <CAD=FV=UtSiueVky6jX2DjQwS58gYU07+0em3jW0juHcDM4K0mg@mail.gmail.com> (raw)
In-Reply-To: <20240502224703.103150-1-swboyd@chromium.org>
Hi,
On Thu, May 2, 2024 at 3:47 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> 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@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>
> ---
>
> This is an alternative approach to [1] which doesn't require any hacks
> to disable clks during driver probe.
>
> [1] https://lore.kernel.org/r/20240327202740.3075378-1-swboyd@chromium.org
>
> drivers/clk/qcom/clk-rcg2.c | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
I'm not even close to an expert on the Qualcomm clock stuff, but the
description of what's going on here seems reasonable to me. I agree
that getting this fixed is important, so I'd be OK with a somewhat
weak:
Reviewed-by: Douglas Anderson <dianders@chromium.org>
...hopefully others more in the know will also review and make sure
it's not going to break anyone's use cases.
next prev parent reply other threads:[~2024-05-02 23:20 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-02 22:47 [PATCH] clk: qcom: Park shared RCGs upon registration Stephen Boyd
2024-05-02 23:20 ` Doug Anderson [this message]
2024-05-10 19:59 ` Nícolas F. R. A. Prado
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAD=FV=UtSiueVky6jX2DjQwS58gYU07+0em3jW0juHcDM4K0mg@mail.gmail.com' \
--to=dianders@chromium.org \
--cc=andersson@kernel.org \
--cc=dmitry.baryshkov@linaro.org \
--cc=laura.nao@collabora.com \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-clk@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mturquette@baylibre.com \
--cc=patches@lists.linux.dev \
--cc=quic_tdas@quicinc.com \
--cc=sboyd@kernel.org \
--cc=swboyd@chromium.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).