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Date: Sat, 14 May 2011 22:30:31 +0200
From: Raffaele Recalcati <lamiaposta71@...il.com>
To: markgross@...gnar.org
Cc: linux-pm@...ts.linux-foundation.org,
davinci-linux-open-source@...ux.davincidsp.com,
linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] pm loss development
On Sat, May 14, 2011 at 6:24 PM, mark gross <markgross@...gnar.org> wrote:
> On Thu, May 12, 2011 at 07:11:01PM +0200, Raffaele Recalcati wrote:
>> What happen normally in runtime pm implementation is that every devices
>> are switched off and are enabled only when needed.
>> In our case instead we have a completely functional embedded system and,
>> when an asyncrhonous event appear, we have only some tens milliseconds
>> before the actual power failure takes place.
>
> Very interesting! I've been worried about a similar failure on battery
> driven devices that can experience significant voltage droops when
> battery gets old, or low, and we turn on the flashlight led, vibrator
> and make the screen bright while a high volume ring tone gets played.
>
> I think 10ms is a bit unrealistic. I think its more like 300uSec before
> you hit brown out.
In our circuit it is the real timing, but I can understand your situation.
Are you sure about 300usec?
>> This patchset add a support in order to switch off not vital part of the system,
>> in order to allow the board to survive longer.
>> This allow the possibility to save important data.
>>
>> The implementation has been written by Davide Ciminaghi.
>> My work instead was about analyzing different previuos implementation,
>> a first completely custom one, a second using runtime pm, arriving
>> finally to that one.
>>
>> I have tested PM loss in our DaVinci dm365 basi board and I write here below a
>> piece of code showing a possible usage.
>>
>> -------------------
>>
>> static int powerfail_status;
>>
>> static irqreturn_t basi_powerfail_stop(int irq, void *dev_id);
>>
>> static irqreturn_t basi_powerfail_quick_check_start(int irq, void *dev_id)
>> {
>> basi_mask_irq_gpio0(IRQ_DM365_GPIO0_2);
>> basi_unmask_irq_gpio0(IRQ_DM365_GPIO0_0);
>>
>> /* PowerFail situation - START: power is going away */
>> return IRQ_WAKE_THREAD;
>> }
>>
>> static irqreturn_t basi_powerfail_start(int irq, void *dev_id)
>> {
>> if (powerfail_status)
>> return IRQ_HANDLED;
>> powerfail_status = 1;
>> pm_loss_power_changed(SYS_PWR_FAILING);
>> return IRQ_HANDLED;
>> }
>>
>>
>> static irqreturn_t basi_powerfail_quick_check_stop(int irq, void *dev_id)
>> {
>> basi_mask_irq_gpio0(IRQ_DM365_GPIO0_0);
>> basi_unmask_irq_gpio0(IRQ_DM365_GPIO0_2);
>>
>> /* PowerFail situation - STOP: power is coming back */
>> return IRQ_WAKE_THREAD;
>> }
>>
>> static irqreturn_t basi_powerfail_stop(int irq, void *dev_id)
>> {
>> if (!powerfail_status)
>> return IRQ_HANDLED;
>> powerfail_status = 0;
>> pm_loss_power_changed(SYS_PWR_GOOD);
>> return IRQ_HANDLED;
>> }
>>
>> enum basi_pwrfail_prio {
>> BASI_PWR_FAIL_PRIO_0,
>> BASI_PWR_FAIL_MIN_PRIO = BASI_PWR_FAIL_PRIO_0,
>> BASI_PWR_FAIL_PRIO_1,
>> BASI_PWR_FAIL_PRIO_2,
>> BASI_PWR_FAIL_PRIO_3,
>> BASI_PWR_FAIL_MAX_PRIO = BASI_PWR_FAIL_PRIO_3,
>> };
>>
>> struct pm_loss_default_policy_item basi_pm_loss_policy_items[] = {
>> {
>> .bus_name = "mmc",
>> .bus_priority = BASI_PWR_FAIL_PRIO_1,
>> },
>> {
>> .bus_name = "platform",
>> .bus_priority = BASI_PWR_FAIL_PRIO_2,
>> },
>> };
>>
>> #define BASI_POLICY_NAME "basi-default"
>>
>> struct pm_loss_default_policy_table basi_pm_loss_policy_table = {
>> .name = BASI_POLICY_NAME,
>> .items = basi_pm_loss_policy_items,
>> .nitems = ARRAY_SIZE(basi_pm_loss_policy_items),
>> };
>>
>> static void basi_powerfail_configure(void)
>> {
>> int stat;
>> struct pm_loss_policy *p;
>> stat = request_threaded_irq(IRQ_DM365_GPIO0_2,
> Is this some comparator device that tugs on this gpio when the voltage
> drops or goes to 0? Is threaded irq fast enough?
yes, there is a comparator.
I need more data about timing, I'll try to add this info in some days.
> Could we consider something that includes a hot path ISR based
> notification call back to do stuff like blink off devices that don't
> need to save state; backlights, vibrators, flashlight LEDs, audio
> output drivers <-- I'm not sure about audio HW, and then a slower path
> for other things that can be put into lower power states?
>
> the all-clear notification that power is good again should be on a
> slower path I would assume.
First I get data, afterwards we can see if your need can be seen as an
extension or something else.
>
> --mark
>
>> basi_powerfail_quick_check_start,
>> basi_powerfail_start,
>> 0,
>> "pwrfail-on", NULL);
>> if (stat < 0)
>> printk(KERN_ERR "request_threaded_irq for IRQ%d (pwrfail-on) "
>> "failed\n", IRQ_DM365_GPIO0_2);
>> stat = request_threaded_irq(IRQ_DM365_GPIO0_0,
>> basi_powerfail_quick_check_stop,
>> basi_powerfail_stop, 0,
>> "pwrfail-off", NULL);
>> if (stat < 0)
>> printk(KERN_ERR "request_threaded_irq for IRQ%d (pwrfail-off) "
>> "failed\n", IRQ_DM365_GPIO0_0);
>> basi_mask_irq_gpio0(IRQ_DM365_GPIO0_0);
>> p = pm_loss_setup_default_policy(&basi_pm_loss_policy_table);
>>
>> if (!p)
>> printk(KERN_ERR "Could not register pwr change policy\n");
>>
>> if (pm_loss_set_policy(BASI_POLICY_NAME) < 0)
>> printk(KERN_ERR "Could not set %s power loss policy\n",
>> BASI_POLICY_NAME);
>> }
>>
>> int platform_pm_loss_power_changed(struct device *dev,
>> enum sys_power_state s)
>> {
>> int ret = 0;
>>
>> /* Calling platform bus pm_loss functions */
>> pr_debug_pm_loss("platform_pm_loss_power_changed(%d)\n", s);
>>
>> if (dev->driver && dev->driver->pm &&
>> dev->driver->pm->power_changed)
>> ret = dev->driver->pm->power_changed(dev, s);
>> return ret;
>> }
>>
>>
>>
>>
>> _______________________________________________
>> linux-pm mailing list
>> linux-pm@...ts.linux-foundation.org
>> https://lists.linux-foundation.org/mailman/listinfo/linux-pm
>
Bye,
Raffaele
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