linux-kernel - Re: [PATCH] drivers: dw_mmc: Replace devm_clk_get with devm_clk_get

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Message-ID: <CAPDyKFqJaojUwGhNPnQXpL7q7MkmtfA7Q-QkDHKj=nVF4YYVCw@mail.gmail.com>
Date: Fri, 23 Jan 2026 10:46:45 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "ping.gao" <ping.gao@...sung.com>
Cc: jh80.chung@...sung.com, sebastian.reichel@...labora.com, 
	shawn.lin@...k-chips.com, linux-mmc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, hy50.seo@...sung.com, kwangwon.min@...sung.com
Subject: Re: [PATCH] drivers: dw_mmc: Replace devm_clk_get with devm_clk_get_optional

On Fri, 23 Jan 2026 at 09:51, ping.gao <ping.gao@...sung.com> wrote:
>
> By using devm_clk_get_optional, if clk is optional for device and not define in dts
> it will return NULL, then clk_prepare_enable/clk_disable_unprepare for biu_clk is safe to
> bail out internally.
>
> before biu_clk in dwmmc driver devm_clk_get fail, but it's ERR_PTR,
> not null,it will panic when call clk_prepare
> log is below:
> [  438.400868] [7:   binder:436_2: 4998] Unable to handle kernel paging request at virtual address fffffffffffffffe
> [  438.400877] [7:   binder:436_2: 4998] Mem abort info:
> [  438.400881] [7:   binder:436_2: 4998]   ESR = 0x0000000096000005
> [  438.400887] [7:   binder:436_2: 4998]   EC = 0x25: DABT (current EL), IL = 32 bits
> [  438.400894] [7:   binder:436_2: 4998]   SET = 0, FnV = 0
> [  438.400899] [7:   binder:436_2: 4998]   EA = 0, S1PTW = 0
> [  438.400904] [7:   binder:436_2: 4998]   FSC = 0x05: level 1 translation fault
> ...
> [  438.409424] [7:   binder:436_2: 4998] Call trace:
> [  438.409429] [7:   binder:436_2: 4998]  clk_prepare+0x10/0x24
> [  438.409439] [7:   binder:436_2: 4998]  dw_mci_runtime_resume+0x50/0x2d8 [dw_mmc_samsung cd210e210975263404c28fc89778f369f8398f0c]
> [  438.409471] [7:   binder:436_2: 4998]  dw_mci_exynos_runtime_resume+0x18/0x58 [dw_mmc_exynos_samsung 2735a594c7c9c9e8c65b0b87523fbf70dcaabfff]
> [  438.409496] [7:   binder:436_2: 4998]  pm_generic_runtime_resume+0x40/0x58
> [  438.409506] [7:   binder:436_2: 4998]  pm_runtime_force_resume+0x9c/0x134
> [  438.409517] [7:   binder:436_2: 4998]  platform_pm_resume+0x40/0x8c
> [  438.409529] [7:   binder:436_2: 4998]  dpm_run_callback+0x64/0x230
> [  438.409540] [7:   binder:436_2: 4998]  __device_resume+0x1d8/0x394
> [  438.409551] [7:   binder:436_2: 4998]  dpm_resume+0x110/0x2b8
> [  438.409561] [7:   binder:436_2: 4998]  dpm_resume_end+0x1c/0x38
> [  438.409570] [7:   binder:436_2: 4998]  suspend_devices_and_enter+0x828/0xab0
> [  438.409582] [7:   binder:436_2: 4998]  pm_suspend+0x334/0x618
> [  438.409592] [7:   binder:436_2: 4998]  state_store+0x104/0x144
> [  438.409601] [7:   binder:436_2: 4998]  kobj_attr_store+0x30/0x48
> [  438.409610] [7:   binder:436_2: 4998]  sysfs_kf_write+0x54/0x6c
> [  438.409619] [7:   binder:436_2: 4998]  kernfs_fop_write_iter+0x104/0x1a8
> [  438.409628] [7:   binder:436_2: 4998]  vfs_write+0x24c/0x2f4
> [  438.409640] [7:   binder:436_2: 4998]  ksys_write+0x78/0xe8
> [  438.409652] [7:   binder:436_2: 4998]  __arm64_sys_write+0x1c/0x2c
> [  438.409664] [7:   binder:436_2: 4998]  invoke_syscall+0x58/0x114
> [  438.409676] [7:   binder:436_2: 4998]  el0_svc_common+0xac/0xe0
> [  438.409687] [7:   binder:436_2: 4998]  do_el0_svc+0x1c/0x28
> [  438.409698] [7:   binder:436_2: 4998]  el0_svc+0x38/0x68
> [  438.409705] [7:   binder:436_2: 4998]  el0t_64_sync_handler+0x68/0xbc
> [  438.409712] [7:   binder:436_2: 4998]  el0t_64_sync+0x1a8/0x1ac
>
> Signed-off-by: ping.gao <ping.gao@...sung.com>

You are not versioning your patches, which makes it difficult for me
to manage them. Again, please read
Documentation/process/submitting-patches.rst before you continue to
post any more patches.

Anyway, I can pick this up as is for now, when Shawn has reviewed it.

Kind regards
Uffe

> ---
>  drivers/mmc/host/dw_mmc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index c5db92bbb094..6bcc1e7233c0 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -3375,7 +3375,7 @@ int dw_mci_probe(struct dw_mci *host)
>                                              "platform data not available\n");
>         }
>
> -       host->biu_clk = devm_clk_get(host->dev, "biu");
> +       host->biu_clk = devm_clk_get_optional(host->dev, "biu");
>         if (IS_ERR(host->biu_clk)) {
>                 dev_dbg(host->dev, "biu clock not available\n");
>                 ret = PTR_ERR(host->biu_clk);
> --
> 2.50.1
>