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Date:   Wed, 30 Aug 2017 15:35:01 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Shawn Lin <shawn.lin@...k-chips.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] driver core: detach device's pm_domain after devres_release_all

On 30 August 2017 at 03:34, Shawn Lin <shawn.lin@...k-chips.com> wrote:
> The intention of this patch is to move dev_pm_domain_detach after
> devres_release_all to avoid possible accessing device's registers
> with genpd been powered off.
>
> Many common IP drivers use devm_request_irq to request irq for either
> shared irq or non-shared irq. So we rely on devres_release_all to
> free irq automatically. However we could see a situation that if the
> driver use devm_request_irq to register a shared irq and unbind the
> driver later, the irq could be triggerd cocurrently just between
> finishing dev_pm_domain_detach and calling devm_irq_release, so that
> driver's ISR should be called and try to access device's register, which
> may hang up the system. The reason is that some SoCs, including Rockchips'
> SoCs, couldn't support accessing controllers' registers w/o clk and power
> domain enabled.
>
> Also we have CONFIG_DEBUG_SHIRQ to theoretically expose this kind of
> problem as devm_free_irq -> __free_irq says: "It's a shared IRQ -- the
> driver ought to be prepared for an IRQ event to happen even now it's being
> freed". That will simulate the aforementioned situation as it fires
> extra irq action to make sure driver/system is robust enough to deal
> with this kind of problem.

Hmm, I think there are a related problem when the device becomes
suspended. We simply need a way to avoid having the irq handler being
called, when the device is suspended.

Please have a look at the following discussion, it concerns an issue
for sdhci during suspend:
https://lkml.org/lkml/2016/1/28/213

I don't think we ended up fixing the problem, but a couple of solution
was discussed. Likely some of them should be able to solve also this
issue, I think.

Kind regards
Uffe

>
> So now we face a two possible choices to fix this by
> (1) either using request_irq and free_irq directly
> (2) or moving dev_pm_domain_detach after devres_release_all which
> makes sure we free the irq before powering off power domain.
>
> However, choice (1) implies that devm_request_irq shouldn't exist
> or at least shouldn't be used for shared irq case. Meanwhile we don't
> know how many drivers have this kind of issue and need to fix. So
> choice (2) makes more sense to me, and that is the reason for why we
> need to fix it like what this patch does.
>
> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
>
> ---
>
> Changes in v3:
> - fix the code path for consolidating the attach for both of driver
>   and bus driver, and then move detach to the error path
> - rework the changelog
>
>  drivers/base/dd.c       | 16 ++++++++++++++++
>  drivers/base/platform.c | 18 ++----------------
>  2 files changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index ad44b40..aea0bb1 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -25,7 +25,9 @@
>  #include <linux/kthread.h>
>  #include <linux/wait.h>
>  #include <linux/async.h>
> +#include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/pm_domain.h>
>  #include <linux/pinctrl/devinfo.h>
>
>  #include "base.h"
> @@ -356,6 +358,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>         int local_trigger_count = atomic_read(&deferred_trigger_count);
>         bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) &&
>                            !drv->suppress_bind_attrs;
> +       struct platform_driver *pdrv;
>
>         if (defer_all_probes) {
>                 /*
> @@ -409,6 +412,16 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>          */
>         devices_kset_move_last(dev);
>
> +       ret = dev_pm_domain_attach(dev, true);
> +       pdrv = to_platform_driver(dev->driver);
> +       /* don't fail if just dev_pm_domain_attach failed */
> +       if (pdrv && pdrv->prevent_deferred_probe &&
> +           ret == -EPROBE_DEFER) {
> +               dev_warn(dev, "probe deferral not supported\n");
> +               ret = -ENXIO;
> +               goto probe_failed;
> +       }
> +
>         if (dev->bus->probe) {
>                 ret = dev->bus->probe(dev);
>                 if (ret)
> @@ -428,6 +441,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>                         drv->remove(dev);
>
>                 devres_release_all(dev);
> +               dev_pm_domain_detach(dev, true);
>                 driver_sysfs_remove(dev);
>                 dev->driver = NULL;
>                 dev_set_drvdata(dev, NULL);
> @@ -458,6 +472,7 @@ static int really_probe(struct device *dev, struct device_driver *drv)
>  pinctrl_bind_failed:
>         device_links_no_driver(dev);
>         devres_release_all(dev);
> +       dev_pm_domain_detach(dev, true);
>         driver_sysfs_remove(dev);
>         dev->driver = NULL;
>         dev_set_drvdata(dev, NULL);
> @@ -864,6 +879,7 @@ static void __device_release_driver(struct device *dev, struct device *parent)
>                 dma_deconfigure(dev);
>
>                 devres_release_all(dev);
> +               dev_pm_domain_detach(dev, true);
>                 dev->driver = NULL;
>                 dev_set_drvdata(dev, NULL);
>                 if (dev->pm_domain && dev->pm_domain->dismiss)
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index d1bd992..8fa688d 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -572,22 +572,8 @@ static int platform_drv_probe(struct device *_dev)
>         if (ret < 0)
>                 return ret;
>
> -       ret = dev_pm_domain_attach(_dev, true);
> -       if (ret != -EPROBE_DEFER) {
> -               if (drv->probe) {
> -                       ret = drv->probe(dev);
> -                       if (ret)
> -                               dev_pm_domain_detach(_dev, true);
> -               } else {
> -                       /* don't fail if just dev_pm_domain_attach failed */
> -                       ret = 0;
> -               }
> -       }
> -
> -       if (drv->prevent_deferred_probe && ret == -EPROBE_DEFER) {
> -               dev_warn(_dev, "probe deferral not supported\n");
> -               ret = -ENXIO;
> -       }
> +       if (drv->probe)
> +               ret = drv->probe(dev);
>
>         return ret;
>  }
> --
> 1.9.1
>
>

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