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Message-id: <fd0f3f8e-fe0e-b75e-620d-ecf6ffff5f69@samsung.com>
Date: Tue, 26 Apr 2016 12:37:38 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
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
Hello,
On 2016-04-25 11:19, Ulf Hansson wrote:
> 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.
I don't think that such micro-optimization makes sense in this case.
Please note that there is still no platform and driver which require
this deferred probe logic - in my case exynos power domain driver is
registered very early, so dev_pm_domain_attach() calls succeeds in the
standard amba device registration path. This patch is mainly to get
the device registered to power domain to properly read its cid/pid
pair.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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