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[ALSA] document - Update PM support

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Modules: Documentation

Update the description about the PCI PM support.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2005-11-17 17:26:09 +01:00 committed by Jaroslav Kysela
parent a4efc230c6
commit 5fe76e4dc6
1 changed files with 146 additions and 39 deletions
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185
Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
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@ -18,8 +18,8 @@
</affiliation>
</author>
<date>October 6, 2005</date>
<edition>0.3.5</edition>
<date>November 17, 2005</date>
<edition>0.3.6</edition>
<abstract>
<para>
@ -2329,9 +2329,14 @@ struct _snd_pcm_runtime {
<constant>PAUSE</constant> bit means that the pcm supports the
<quote>pause</quote> operation, while the
<constant>RESUME</constant> bit means that the pcm supports
the <quote>suspend/resume</quote> operation. If these flags
are set, the <structfield>trigger</structfield> callback below
must handle the corresponding commands.
the full <quote>suspend/resume</quote> operation.
If <constant>PAUSE</constant> flag is set,
the <structfield>trigger</structfield> callback below
must handle the corresponding (pause push/release) commands.
The suspend/resume trigger commands can be defined even without
<constant>RESUME</constant> flag. See <link
linkend="power-management"><citetitle>
Power Management</citetitle></link> section for details.
</para>
<para>
@ -2903,8 +2908,8 @@ struct _snd_pcm_runtime {
</para>
<para>
When the pcm supports the suspend/resume operation
(i.e. <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set),
When the pcm supports the suspend/resume operation,
regardless of full or partial suspend/resume support,
<constant>SUSPEND</constant> and <constant>RESUME</constant>
commands must be handled, too.
These commands are issued when the power-management status is
@ -2913,6 +2918,8 @@ struct _snd_pcm_runtime {
do suspend and resume of the pcm substream, and usually, they
are identical with <constant>STOP</constant> and
<constant>START</constant> commands, respectively.
See <link linkend="power-management"><citetitle>
Power Management</citetitle></link> section for details.
</para>
<para>
@ -5483,22 +5490,60 @@ struct _snd_pcm_runtime {
<constant>CONFIG_PM</constant>.
</para>
<para>
If the driver supports the suspend/resume
<emphasis>fully</emphasis>, that is, the device can be
properly resumed to the status at the suspend is called,
you can set <constant>SNDRV_PCM_INFO_RESUME</constant> flag
to pcm info field. Usually, this is possible when the
registers of ths chip can be safely saved and restored to the
RAM. If this is set, the trigger callback is called with
<constant>SNDRV_PCM_TRIGGER_RESUME</constant> after resume
callback is finished.
</para>
<para>
Even if the driver doesn't support PM fully but only the
partial suspend/resume is possible, it's still worthy to
implement suspend/resume callbacks. In such a case, applications
would reset the status by calling
<function>snd_pcm_prepare()</function> and restart the stream
appropriately. Hence, you can define suspend/resume callbacks
below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant>
info flag to the PCM.
</para>
<para>
Note that the trigger with SUSPEND can be always called when
<function>snd_pcm_suspend_all</function> is called,
regardless of <constant>SNDRV_PCM_INFO_RESUME</constant> flag.
The <constant>RESUME</constant> flag affects only the behavior
of <function>snd_pcm_resume()</function>.
(Thus, in theory,
<constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed
to be handled in the trigger callback when no
<constant>SNDRV_PCM_INFO_RESUME</constant> flag is set. But,
it's better to keep it for compatibility reason.)
</para>
<para>
ALSA provides the common power-management layer. Each card driver
needs to have only low-level suspend and resume callbacks.
In the earlier version of ALSA drivers, a common
power-management layer was provided, but it has been removed.
The driver needs to define the suspend/resume hooks according to
the bus the device is assigned. In the case of PCI driver, the
callbacks look like below:
<informalexample>
<programlisting>
<![CDATA[
#ifdef CONFIG_PM
static int snd_my_suspend(struct snd_card *card, pm_message_t state)
static int snd_my_suspend(struct pci_dev *pci, pm_message_t state)
{
.... // do things for suspsend
.... /* do things for suspsend */
return 0;
}
static int snd_my_resume(struct snd_card *card)
static int snd_my_resume(struct pci_dev *pci)
{
.... // do things for suspsend
.... /* do things for suspsend */
return 0;
}
#endif
@ -5511,11 +5556,18 @@ struct _snd_pcm_runtime {
The scheme of the real suspend job is as following.
<orderedlist>
<listitem><para>Retrieve the chip data from pm_private_data field.</para></listitem>
<listitem><para>Retrieve the card and the chip data.</para></listitem>
<listitem><para>Call <function>snd_power_change_state()</function> with
<constant>SNDRV_CTL_POWER_D3hot</constant> to change the
power status.</para></listitem>
<listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem>
<listitem><para>If AC97 codecs are used, call
<function>snd_ac97_resume()</function> for each codec.</para></listitem>
<listitem><para>Save the register values if necessary.</para></listitem>
<listitem><para>Stop the hardware if necessary.</para></listitem>
<listitem><para>Disable the PCI device by calling <function>pci_disable_device()</function>.</para></listitem>
<listitem><para>Disable the PCI device by calling
<function>pci_disable_device()</function>. Then, call
<function>pci_save_state()</function> at last.</para></listitem>
</orderedlist>
</para>
@ -5525,18 +5577,24 @@ struct _snd_pcm_runtime {
<informalexample>
<programlisting>
<![CDATA[
static int mychip_suspend(struct snd_card *card, pm_message_t state)
static int mychip_suspend(strut pci_dev *pci, pm_message_t state)
{
/* (1) */
struct mychip *chip = card->pm_private_data;
struct snd_card *card = pci_get_drvdata(pci);
struct mychip *chip = card->private_data;
/* (2) */
snd_pcm_suspend_all(chip->pcm);
snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
/* (3) */
snd_mychip_save_registers(chip);
snd_pcm_suspend_all(chip->pcm);
/* (4) */
snd_mychip_stop_hardware(chip);
snd_ac97_suspend(chip->ac97);
/* (5) */
pci_disable_device(chip->pci);
snd_mychip_save_registers(chip);
/* (6) */
snd_mychip_stop_hardware(chip);
/* (7) */
pci_disable_device(pci);
pci_save_state(pci);
return 0;
}
]]>
@ -5548,14 +5606,17 @@ struct _snd_pcm_runtime {
The scheme of the real resume job is as following.
<orderedlist>
<listitem><para>Retrieve the chip data from pm_private_data field.</para></listitem>
<listitem><para>Enable the pci device again by calling
<function>pci_enable_device()</function>.</para></listitem>
<listitem><para>Retrieve the card and the chip data.</para></listitem>
<listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>.
Then enable the pci device again by calling <function>pci_enable_device()</function>.
Call <function>pci_set_master()</function> if necessary, too.</para></listitem>
<listitem><para>Re-initialize the chip.</para></listitem>
<listitem><para>Restore the saved registers if necessary.</para></listitem>
<listitem><para>Resume the mixer, e.g. calling
<function>snd_ac97_resume()</function>.</para></listitem>
<listitem><para>Restart the hardware (if any).</para></listitem>
<listitem><para>Call <function>snd_power_change_state()</function> with
<constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem>
</orderedlist>
</para>
@ -5565,12 +5626,15 @@ struct _snd_pcm_runtime {
<informalexample>
<programlisting>
<![CDATA[
static void mychip_resume(struct mychip *chip)
static int mychip_resume(struct pci_dev *pci)
{
/* (1) */
struct mychip *chip = card->pm_private_data;
struct snd_card *card = pci_get_drvdata(pci);
struct mychip *chip = card->private_data;
/* (2) */
pci_enable_device(chip->pci);
pci_restore_state(pci);
pci_enable_device(pci);
pci_set_master(pci);
/* (3) */
snd_mychip_reinit_chip(chip);
/* (4) */
@ -5579,6 +5643,8 @@ struct _snd_pcm_runtime {
snd_ac97_resume(chip->ac97);
/* (6) */
snd_mychip_restart_chip(chip);
/* (7) */
snd_power_change_state(card, SNDRV_CTL_POWER_D0);
return 0;
}
]]>
@ -5587,8 +5653,23 @@ struct _snd_pcm_runtime {
</para>
<para>
OK, we have all callbacks now. Let's set up them now. In the
initialization of the card, add the following:
As shown in the above, it's better to save registers after
suspending the PCM operations via
<function>snd_pcm_suspend_all()</function> or
<function>snd_pcm_suspend()</function>. It means that the PCM
streams are already stoppped when the register snapshot is
taken. But, remind that you don't have to restart the PCM
stream in the resume callback. It'll be restarted via
trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant>
when necessary.
</para>
<para>
OK, we have all callbacks now. Let's set them up. In the
initialization of the card, make sure that you can get the chip
data from the card instance, typically via
<structfield>private_data</structfield> field, in case you
created the chip data individually.
<informalexample>
<programlisting>
@ -5600,30 +5681,53 @@ struct _snd_pcm_runtime {
struct snd_card *card;
struct mychip *chip;
....
snd_card_set_pm_callback(card, snd_my_suspend, snd_my_resume, chip);
card = snd_card_new(index[dev], id[dev], THIS_MODULE, NULL);
....
chip = kzalloc(sizeof(*chip), GFP_KERNEL);
....
card->private_data = chip;
....
}
]]>
</programlisting>
</informalexample>
When you created the chip data with
<function>snd_card_new()</function>, it's anyway accessible
via <structfield>private_data</structfield> field.
<informalexample>
<programlisting>
<![CDATA[
static int __devinit snd_mychip_probe(struct pci_dev *pci,
const struct pci_device_id *pci_id)
{
....
struct snd_card *card;
struct mychip *chip;
....
card = snd_card_new(index[dev], id[dev], THIS_MODULE,
sizeof(struct mychip));
....
chip = card->private_data;
....
}
]]>
</programlisting>
</informalexample>
Here you don't have to put ifdef CONFIG_PM around, since it's already
checked in the header and expanded to empty if not needed.
</para>
<para>
If you need a space for saving the registers, you'll need to
allocate the buffer for it here, too, since it would be fatal
If you need a space for saving the registers, allocate the
buffer for it here, too, since it would be fatal
if you cannot allocate a memory in the suspend phase.
The allocated buffer should be released in the corresponding
destructor.
</para>
<para>
And next, set suspend/resume callbacks to the pci_driver,
This can be done by passing a macro SND_PCI_PM_CALLBACKS
in the pci_driver struct. This macro is expanded to the correct
(global) callbacks if CONFIG_PM is set.
And next, set suspend/resume callbacks to the pci_driver.
<informalexample>
<programlisting>
@ -5633,7 +5737,10 @@ struct _snd_pcm_runtime {
.id_table = snd_my_ids,
.probe = snd_my_probe,
.remove = __devexit_p(snd_my_remove),
SND_PCI_PM_CALLBACKS
#ifdef CONFIG_PM
.suspend = snd_my_suspend,
.resume = snd_my_resume,
#endif
};
]]>
</programlisting>