linux-kernel - Re: [PATCH v4 1/5] clk: qcom: ipq5018: keep XO clock always on

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Message-ID:
 <BL4PR19MB8902AFEA7DCC8C41B7C2C6569D72A@BL4PR19MB8902.namprd19.prod.outlook.com>
Date: Wed, 18 Jun 2025 14:03:24 +0400
From: George Moussalem <george.moussalem@...look.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Luo Jie <quic_luoj@...cinc.com>,
 Lee Jones <lee@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>,
 Arnd Bergmann <arnd@...db.de>, linux-arm-msm@...r.kernel.org,
 linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/5] clk: qcom: ipq5018: keep XO clock always on

Hi Bjorn,

On 6/18/25 07:33, Bjorn Andersson wrote:
> On Fri, May 16, 2025 at 04:36:08PM +0400, George Moussalem via B4 Relay wrote:
>> From: George Moussalem <george.moussalem@...look.com>
>>
>> The XO clock must not be disabled to avoid the kernel trying to disable
>> the it. As such, keep the XO clock always on by flagging it as critical.
>>
> 
> Is there any reason for us to model this clock in Linux, if we're not
> allowed to touch it?
> 
> CLK_IS_CRITICAL has side effect on the runtime PM state of the clock
> controller, so would be nice if we can avoid that.

see discussion here in v2:
https://patchwork.kernel.org/project/linux-arm-msm/patch/20250506-ipq5018-cmn-pll-v2-1-c0a9fcced114@outlook.com/

we explored removing the structs for xo and xo_src and updating the
parent clocks that relied on them, which worked. But the recommendation
eventually was to go for this flag.

> 
> Regards,
> Bjorn
> 
>> Signed-off-by: George Moussalem <george.moussalem@...look.com>
>> ---
>> The kernel will panic when parenting it under the CMN PLL reference
>> clock and the below message will appear in the kernel logs.
>>
>> [    0.916515] ------------[ cut here ]------------
>> [    0.918890] gcc_xo_clk_src status stuck at 'on'
>> [    0.918944] WARNING: CPU: 0 PID: 8 at drivers/clk/qcom/clk-branch.c:86 clk_branch_wait+0x114/0x124
>> [    0.927926] Modules linked in:
>> [    0.936945] CPU: 0 PID: 8 Comm: kworker/0:0 Not tainted 6.6.74 #0
>> [    0.939982] Hardware name: Linksys MX2000 (DT)
>> [    0.946151] Workqueue: pm pm_runtime_work
>> [    0.950489] pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> [    0.954566] pc : clk_branch_wait+0x114/0x124
>> [    0.961335] lr : clk_branch_wait+0x114/0x124
>> [    0.965849] sp : ffffffc08181bb50
>> [    0.970101] x29: ffffffc08181bb50 x28: 0000000000000000 x27: 61c8864680b583eb
>> [    0.973317] x26: ffffff801fec2168 x25: ffffff800000abc0 x24: 0000000000000002
>> [    0.980437] x23: ffffffc0809f6fd8 x22: 0000000000000000 x21: ffffffc08044193c
>> [    0.985276] loop: module loaded
>> [    0.987554] x20: 0000000000000000 x19: ffffffc081749278 x18: 000000000000007c
>> [    0.987573] x17: 0000000091706274 x16: 000000001985c4f7 x15: ffffffc0816bbdf0
>> [    0.987587] x14: 0000000000000174 x13: 000000000000007c x12: 00000000ffffffea
>> [    0.987601] x11: 00000000ffffefff x10: ffffffc081713df0 x9 : ffffffc0816bbd98
>> [    0.987615] x8 : 0000000000017fe8 x7 : c0000000ffffefff x6 : 0000000000057fa8
>> [    1.026268] x5 : 0000000000000fff x4 : 0000000000000000 x3 : ffffffc08181b950
>> [    1.033385] x2 : ffffffc0816bbd30 x1 : ffffffc0816bbd30 x0 : 0000000000000023
>> [    1.040507] Call trace:
>> [    1.047618]  clk_branch_wait+0x114/0x124
>> [    1.049875]  clk_branch2_disable+0x2c/0x3c
>> [    1.054043]  clk_core_disable+0x60/0xac
>> [    1.057948]  clk_core_disable+0x68/0xac
>> [    1.061681]  clk_disable+0x30/0x4c
>> [    1.065499]  pm_clk_suspend+0xd4/0xfc
>> [    1.068971]  pm_generic_runtime_suspend+0x2c/0x44
>> [    1.072705]  __rpm_callback+0x40/0x1bc
>> [    1.077392]  rpm_callback+0x6c/0x78
>> [    1.081038]  rpm_suspend+0xf0/0x5c0
>> [    1.084423]  pm_runtime_work+0xf0/0xfc
>> [    1.087895]  process_one_work+0x17c/0x2f8
>> [    1.091716]  worker_thread+0x2e8/0x4d4
>> [    1.095795]  kthread+0xdc/0xe0
>> [    1.099440]  ret_from_fork+0x10/0x20
>> [    1.102480] ---[ end trace 0000000000000000 ]---
>> ---
>>  drivers/clk/qcom/gcc-ipq5018.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/clk/qcom/gcc-ipq5018.c b/drivers/clk/qcom/gcc-ipq5018.c
>> index 70f5dcb96700f55da1fb19fc893d22350a7e63bf..24eb4c40da63462077ee2e5714e838aa30ced2e3 100644
>> --- a/drivers/clk/qcom/gcc-ipq5018.c
>> +++ b/drivers/clk/qcom/gcc-ipq5018.c
>> @@ -1371,7 +1371,7 @@ static struct clk_branch gcc_xo_clk = {
>>  				&gcc_xo_clk_src.clkr.hw,
>>  			},
>>  			.num_parents = 1,
>> -			.flags = CLK_SET_RATE_PARENT,
>> +			.flags = CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
>>  			.ops = &clk_branch2_ops,
>>  		},
>>  	},
>>
>> -- 
>> 2.49.0
>>
>>

Best regards,
George