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Message-ID: <CAPDyKFqnnjdQgXNjA30AAi--+0NP74gWFjuYfrsvUGTV=yK=Hw@mail.gmail.com>
Date: Mon, 25 Apr 2016 11:19:26 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Russell King - ARM Linux <linux@....linux.org.uk>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Krzysztof Kozlowski <k.kozlowski@...sung.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v8] drivers: amba: properly handle devices with power domains
On 15 April 2016 at 11:13, Marek Szyprowski <m.szyprowski@...sung.com> wrote:
> To read pid/cid registers, the probed device need to be properly turned on.
> When it is inside a power domain, the bus code should ensure that the
> given power domain is enabled before trying to access device's registers.
> However in some cases power domain (or clocks) might not be yet available.
> Returning -EPROBE_DEFER is not a solution in such case, because callers
> don't handle this special error code. Instead such devices are added to the
> special list and their registration is retried from periodic worker until
> all resources are available.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
> Changelog:
>
> v8:
> - replaced notifier with periodic workqueue on Greg request
>
> v7: https://lkml.org/lkml/2016/4/13/201
> - replaced late_initcall approach with a notifier registered to device core
>
> v6: https://lkml.org/lkml/2016/4/12/414
> - got back to v1-style approach on Russell King request to avoid ABI break
> - use list for storing deferred devices and retry their registration from
> late_initcall
>
> v5: https://lkml.org/lkml/2016/2/10/179
> - added 2 more patches to avoid regression with existing drivers (nvdimm and
> sa1111), for more information, see https://lkml.org/lkml/2015/12/17/390
> - changed thread name to "AMBA: add complete support for power domains"
>
> v4: https://lkml.org/lkml/2015/12/2/52
> - fixed more issues pointed by Ulf Hansson and Russell King
>
> v3: https://lkml.org/lkml/2015/12/1/334
> - fixed issues pointed by Ulf Hansson
> - dropped patch for exynos4210 dts, because it already got queued for merging
>
> v2: https://lkml.org/lkml/2015/11/26/229
> - added 2 patches from 'On-demand device probing' thread
> (https://lkml.org/lkml/2015/9/29/189), which move PID/CIR reading
> from amba_device_add() to amba_match()
> - moved dev_pm_domain_attach() to amba_match(), which is allowed to
> return -EPROBE_DEFER
>
> v1: http://www.spinics.net/lists/arm-kernel/msg463185.html
> - initial version
> ---
> drivers/amba/bus.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 90 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index f0099360039e..a5b5c87e2114 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -336,16 +336,7 @@ static void amba_device_release(struct device *dev)
> kfree(d);
> }
>
> -/**
> - * amba_device_add - add a previously allocated AMBA device structure
> - * @dev: AMBA device allocated by amba_device_alloc
> - * @parent: resource parent for this devices resources
> - *
> - * Claim the resource, and read the device cell ID if not already
> - * initialized. Register the AMBA device with the Linux device
> - * manager.
> - */
> -int amba_device_add(struct amba_device *dev, struct resource *parent)
> +static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
> {
> u32 size;
> void __iomem *tmp;
> @@ -373,6 +364,12 @@ int amba_device_add(struct amba_device *dev, struct resource *parent)
> goto err_release;
> }
>
> + ret = dev_pm_domain_attach(&dev->dev, true);
> + if (ret == -EPROBE_DEFER) {
> + iounmap(tmp);
> + goto err_release;
> + }
> +
> ret = amba_get_enable_pclk(dev);
> if (ret == 0) {
> u32 pid, cid;
> @@ -398,6 +395,7 @@ int amba_device_add(struct amba_device *dev, struct resource *parent)
> }
>
> iounmap(tmp);
> + dev_pm_domain_detach(&dev->dev, true);
>
> if (ret)
> goto err_release;
> @@ -421,6 +419,88 @@ int amba_device_add(struct amba_device *dev, struct resource *parent)
> err_out:
> return ret;
> }
> +
> +/*
> + * Registration of AMBA device require reading its pid and cid registers.
> + * To do this, the device must be turned on (if it is a part of power domain)
> + * and have clocks enabled. However in some cases those resources might not be
> + * yet available. Returning EPROBE_DEFER is not a solution in such case,
> + * because callers don't handle this special error code. Instead such devices
> + * are added to the special list and their registration is retried from
> + * periodic worker, until all resources are available and registration succeeds.
> + */
> +struct deferred_device {
> + struct amba_device *dev;
> + struct resource *parent;
> + struct list_head node;
> +};
> +
> +static LIST_HEAD(deferred_devices);
> +static DEFINE_MUTEX(deferred_devices_lock);
> +
> +static void amba_deferred_retry_func(struct work_struct *dummy);
> +static DECLARE_DELAYED_WORK(deferred_retry_work, amba_deferred_retry_func);
> +
> +#define DEFERRED_DEVICE_TIMEOUT (msecs_to_jiffies(5 * 1000))
> +
> +static void amba_deferred_retry_func(struct work_struct *dummy)
> +{
> + struct deferred_device *ddev, *tmp;
> +
> + mutex_lock(&deferred_devices_lock);
> +
> + list_for_each_entry_safe(ddev, tmp, &deferred_devices, node) {
> + int ret = amba_device_try_add(ddev->dev, ddev->parent);
> +
> + if (ret == -EPROBE_DEFER)
> + continue;
> +
> + list_del_init(&ddev->node);
> + kfree(ddev);
> + }
> +
> + if (!list_empty(&deferred_devices))
> + schedule_delayed_work(&deferred_retry_work,
> + DEFERRED_DEVICE_TIMEOUT);
> +
> + mutex_unlock(&deferred_devices_lock);
> +}
> +
> +/**
> + * amba_device_add - add a previously allocated AMBA device structure
> + * @dev: AMBA device allocated by amba_device_alloc
> + * @parent: resource parent for this devices resources
> + *
> + * Claim the resource, and read the device cell ID if not already
> + * initialized. Register the AMBA device with the Linux device
> + * manager.
> + */
> +int amba_device_add(struct amba_device *dev, struct resource *parent)
> +{
> + int ret = amba_device_try_add(dev, parent);
> +
> + if (ret == -EPROBE_DEFER) {
> + struct deferred_device *ddev;
> +
> + ddev = kmalloc(sizeof(*ddev), GFP_KERNEL);
> + if (!ddev)
> + return -ENOMEM;
> +
> + ddev->dev = dev;
> + ddev->parent = parent;
> + ret = 0;
> +
> + mutex_lock(&deferred_devices_lock);
> +
> + if (list_empty(&deferred_devices))
> + schedule_delayed_work(&deferred_retry_work,
> + DEFERRED_DEVICE_TIMEOUT);
> + list_add_tail(&ddev->node, &deferred_devices);
> +
> + mutex_unlock(&deferred_devices_lock);
> + }
> + return ret;
> +}
> EXPORT_SYMBOL_GPL(amba_device_add);
>
> static struct amba_device *
> --
> 1.9.2
>
Overall this looks okay to me! Even if I don't really like the
approach, it seems like this is the only viable option there is right
now.
One minor improvement that I could think of, is to use also a late
initcall in conjunction with the delayed work. So, instead of
scheduling a work unconditionally when -EPROBE_DEFER is returned from
amba_device_try_add(), you can postpone the *first* re-try to be done
from a late initcall.
Of course, as devices may be added also after the late initcall, you
need to keep a flag which tells amba_device_add() whether it can rely
on the late initcall to re-try, or if it needs to schedule a work by
itself.
Kind regards
Uffe
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