From: Claudiu Beznea <[email protected]>
Hi,
Series adds runtime PM support for the ravb driver. This is a continuation
of [1].
There are 4 more preparation patches (patches 1-4) and patch 5
adds runtime PM support.
Patches in this series were part of [2].
Change in v2:
- address review comments
- in patch 4/5 take into account the latest changes introduced
in ravb_set_features_gbeth()
Changes since [2]:
- patch 1/5 is new
- use pm_runtime_get_noresume() and pm_runtime_active() in patches
3/5, 4/5
- fixed higlighted typos in patch 4/5
[1] https://lore.kernel.org/all/[email protected]/
[2] https://lore.kernel.org/all/[email protected]/
Claudiu Beznea (5):
net: ravb: Get rid of the temporary variable irq
net: ravb: Keep the reverse order of operations in ravb_close()
net: ravb: Return cached statistics if the interface is down
net: ravb: Do not apply RX checksum settings to hardware if the
interface is down
net: ravb: Add runtime PM support
drivers/net/ethernet/renesas/ravb_main.c | 131 ++++++++++++++++++-----
1 file changed, 105 insertions(+), 26 deletions(-)
--
2.39.2
From: Claudiu Beznea <[email protected]>
Do not apply the RX checksum settings to hardware if the interface is down.
In case runtime PM is enabled, and while the interface is down, the IP will
be in reset mode (as for some platforms disabling the clocks will switch
the IP to reset mode, which will lead to losing register contents) and
applying settings in reset mode is not an option. Instead, cache the RX
checksum settings and apply them in ravb_open() through ravb_emac_init().
This has been solved by introducing pm_runtime_active() check. The device
runtime PM usage counter has been incremented to avoid disabling the device
clocks while the check is in progress (if any).
Commit prepares for the addition of runtime PM.
Signed-off-by: Claudiu Beznea <[email protected]>
---
Changes in v2:
- fixed typo in patch description
- adjusted ravb_set_features_gbeth(); didn't collect the Sergey's Rb
tag due to this
Changes since [2]:
- use pm_runtime_get_noresume() and pm_runtime_active() and updated the
commit message to describe that
- fixed typos
- s/CSUM/checksum in patch title and description
Changes in v3 of [2]:
- this was patch 20/21 in v2
- fixed typos in patch description
- removed code from ravb_open()
- use ndev->flags & IFF_UP checks instead of netif_running()
Changes in v2 of [2]:
- none; this patch is new
[2] https://lore.kernel.org/all/[email protected]/
drivers/net/ethernet/renesas/ravb_main.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index 7a7f743a1fef..f4be08f0198d 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2478,8 +2478,14 @@ static int ravb_change_mtu(struct net_device *ndev, int new_mtu)
static void ravb_set_rx_csum(struct net_device *ndev, bool enable)
{
struct ravb_private *priv = netdev_priv(ndev);
+ struct device *dev = &priv->pdev->dev;
unsigned long flags;
+ pm_runtime_get_noresume(dev);
+
+ if (!pm_runtime_active(dev))
+ goto out_rpm_put;
+
spin_lock_irqsave(&priv->lock, flags);
/* Disable TX and RX */
@@ -2492,6 +2498,9 @@ static void ravb_set_rx_csum(struct net_device *ndev, bool enable)
ravb_rcv_snd_enable(ndev);
spin_unlock_irqrestore(&priv->lock, flags);
+
+out_rpm_put:
+ pm_runtime_put_noidle(dev);
}
static int ravb_endisable_csum_gbeth(struct net_device *ndev, enum ravb_reg reg,
@@ -2515,10 +2524,16 @@ static int ravb_set_features_gbeth(struct net_device *ndev,
{
netdev_features_t changed = ndev->features ^ features;
struct ravb_private *priv = netdev_priv(ndev);
+ struct device *dev = &priv->pdev->dev;
unsigned long flags;
int ret = 0;
u32 val;
+ pm_runtime_get_noresume(dev);
+
+ if (!pm_runtime_active(dev))
+ goto out_rpm_put;
+
spin_lock_irqsave(&priv->lock, flags);
if (changed & NETIF_F_RXCSUM) {
if (features & NETIF_F_RXCSUM)
@@ -2542,9 +2557,12 @@ static int ravb_set_features_gbeth(struct net_device *ndev,
goto done;
}
- ndev->features = features;
done:
spin_unlock_irqrestore(&priv->lock, flags);
+out_rpm_put:
+ pm_runtime_put_noidle(dev);
+ if (!ret)
+ ndev->features = features;
return ret;
}
--
2.39.2
From: Claudiu Beznea <[email protected]>
Keep the reverse order of operations in ravb_close() when compared with
ravb_open(). This is the recommended configuration sequence.
Signed-off-by: Claudiu Beznea <[email protected]>
Reviewed-by: Sergey Shtylyov <[email protected]>
---
Changes in v2:
- none
Changes since [2]:
- none
Changes in v3 of [2]:
- fixed typos in patch description
- collected tags
Changes in v2 of [2]:
- none; this patch is new
[2] https://lore.kernel.org/all/[email protected]/
drivers/net/ethernet/renesas/ravb_main.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index a1bf54de0e4c..c81cbd81826e 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2321,6 +2321,14 @@ static int ravb_close(struct net_device *ndev)
ravb_write(ndev, 0, RIC2);
ravb_write(ndev, 0, TIC);
+ /* PHY disconnect */
+ if (ndev->phydev) {
+ phy_stop(ndev->phydev);
+ phy_disconnect(ndev->phydev);
+ if (of_phy_is_fixed_link(np))
+ of_phy_deregister_fixed_link(np);
+ }
+
/* Stop PTP Clock driver */
if (info->gptp || info->ccc_gac)
ravb_ptp_stop(ndev);
@@ -2339,14 +2347,6 @@ static int ravb_close(struct net_device *ndev)
}
}
- /* PHY disconnect */
- if (ndev->phydev) {
- phy_stop(ndev->phydev);
- phy_disconnect(ndev->phydev);
- if (of_phy_is_fixed_link(np))
- of_phy_deregister_fixed_link(np);
- }
-
cancel_work_sync(&priv->work);
if (info->nc_queues)
--
2.39.2
From: Claudiu Beznea <[email protected]>
Return the cached statistics in case the interface is down. There should be
no drawback to this, as cached statistics are updated in ravb_close().
In order to avoid accessing the IP registers while the IP is runtime
suspended pm_runtime_active() check was introduced. The device runtime
PM usage counter has been incremented to avoid disabling the device clocks
while the check is in progress (if any).
The commit prepares the code for the addition of runtime PM support.
Suggested-by: Sergey Shtylyov <[email protected]>
Signed-off-by: Claudiu Beznea <[email protected]>
Reviewed-by: Sergey Shtylyov <[email protected]>
---
Changes in v2:
- collected tag
Changes since [2]:
- use pm_runtime_get_noresume() and pm_runtime_active()
Changes in v3 of [2]:
- this was patch 18/21 in v2
- use ndev->flags & IFF_UP instead of netif_running checks
Changes in v2 of [2]:
- none; this patch is new
[2] https://lore.kernel.org/all/[email protected]/
drivers/net/ethernet/renesas/ravb_main.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index c81cbd81826e..7a7f743a1fef 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -2248,8 +2248,15 @@ static struct net_device_stats *ravb_get_stats(struct net_device *ndev)
struct ravb_private *priv = netdev_priv(ndev);
const struct ravb_hw_info *info = priv->info;
struct net_device_stats *nstats, *stats0, *stats1;
+ struct device *dev = &priv->pdev->dev;
nstats = &ndev->stats;
+
+ pm_runtime_get_noresume(dev);
+
+ if (!pm_runtime_active(dev))
+ goto out_rpm_put;
+
stats0 = &priv->stats[RAVB_BE];
if (info->tx_counters) {
@@ -2291,6 +2298,8 @@ static struct net_device_stats *ravb_get_stats(struct net_device *ndev)
nstats->rx_over_errors += stats1->rx_over_errors;
}
+out_rpm_put:
+ pm_runtime_put_noidle(dev);
return nstats;
}
@@ -2358,6 +2367,9 @@ static int ravb_close(struct net_device *ndev)
if (info->nc_queues)
ravb_ring_free(ndev, RAVB_NC);
+ /* Update statistics. */
+ ravb_get_stats(ndev);
+
/* Set reset mode. */
return ravb_set_opmode(ndev, CCC_OPC_RESET);
}
--
2.39.2
From: Claudiu Beznea <[email protected]>
Add runtime PM support for the ravb driver. As the driver is used by
different IP variants, with different behaviors, to be able to have the
runtime PM support available for all devices, the preparatory commits
moved all the resources parsing and allocations in the driver's probe
function and kept the settings for ravb_open(). This is due to the fact
that on some IP variants-platforms tuples disabling/enabling the clocks
will switch the IP to the reset operation mode where registers' content is
lost and reconfiguration needs to be done. For this the rabv_open()
function enables the clocks, switches the IP to configuration mode, applies
all the registers settings and switches the IP to the operational mode. At
the end of ravb_open() IP is ready to send/receive data.
In ravb_close() necessary reverts are done (compared with ravb_open()), the
IP is switched to reset mode and clocks are disabled.
The ethtool APIs or IOCTLs that might execute while the interface is down
are either cached (and applied in ravb_open()) or rejected (as at that time
the IP is in reset mode). Keeping the IP in the reset mode also increases
the power saved (according to the hardware manual).
Signed-off-by: Claudiu Beznea <[email protected]>
Reviewed-by: Sergey Shtylyov <[email protected]>
---
Changes in v2:
- none
Changes since [2]:
- none
- didn't returned directly the ret code of pm_runtime_put_autosuspend()
as, in theory, it might return 1 in case device is suspended through
this calltrace:
pm_runtime_put_autosuspend() ->
__pm_runtime_suspend() ->
rpm_suspend() ->
rpm_check_suspend_allowed()
Changes in v3 of [2]:
- this was patch 21/21 in v2
- collected tags
- fixed typos in patch description
Changes in v2 of [2]:
- keep RPM support for all platforms
[2] https://lore.kernel.org/all/[email protected]/
drivers/net/ethernet/renesas/ravb_main.c | 54 ++++++++++++++++++++++--
1 file changed, 50 insertions(+), 4 deletions(-)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index f4be08f0198d..5bbfdfeef8a9 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -1939,16 +1939,21 @@ static int ravb_open(struct net_device *ndev)
{
struct ravb_private *priv = netdev_priv(ndev);
const struct ravb_hw_info *info = priv->info;
+ struct device *dev = &priv->pdev->dev;
int error;
napi_enable(&priv->napi[RAVB_BE]);
if (info->nc_queues)
napi_enable(&priv->napi[RAVB_NC]);
+ error = pm_runtime_resume_and_get(dev);
+ if (error < 0)
+ goto out_napi_off;
+
/* Set AVB config mode */
error = ravb_set_config_mode(ndev);
if (error)
- goto out_napi_off;
+ goto out_rpm_put;
ravb_set_delay_mode(ndev);
ravb_write(ndev, priv->desc_bat_dma, DBAT);
@@ -1982,6 +1987,9 @@ static int ravb_open(struct net_device *ndev)
ravb_stop_dma(ndev);
out_set_reset:
ravb_set_opmode(ndev, CCC_OPC_RESET);
+out_rpm_put:
+ pm_runtime_mark_last_busy(dev);
+ pm_runtime_put_autosuspend(dev);
out_napi_off:
if (info->nc_queues)
napi_disable(&priv->napi[RAVB_NC]);
@@ -2322,6 +2330,8 @@ static int ravb_close(struct net_device *ndev)
struct ravb_private *priv = netdev_priv(ndev);
const struct ravb_hw_info *info = priv->info;
struct ravb_tstamp_skb *ts_skb, *ts_skb2;
+ struct device *dev = &priv->pdev->dev;
+ int error;
netif_tx_stop_all_queues(ndev);
@@ -2371,7 +2381,14 @@ static int ravb_close(struct net_device *ndev)
ravb_get_stats(ndev);
/* Set reset mode. */
- return ravb_set_opmode(ndev, CCC_OPC_RESET);
+ error = ravb_set_opmode(ndev, CCC_OPC_RESET);
+ if (error)
+ return error;
+
+ pm_runtime_mark_last_busy(dev);
+ pm_runtime_put_autosuspend(dev);
+
+ return 0;
}
static int ravb_hwtstamp_get(struct net_device *ndev, struct ifreq *req)
@@ -2931,6 +2948,8 @@ static int ravb_probe(struct platform_device *pdev)
clk_prepare(priv->refclk);
platform_set_drvdata(pdev, ndev);
+ pm_runtime_set_autosuspend_delay(&pdev->dev, 100);
+ pm_runtime_use_autosuspend(&pdev->dev);
pm_runtime_enable(&pdev->dev);
error = pm_runtime_resume_and_get(&pdev->dev);
if (error < 0)
@@ -3036,6 +3055,9 @@ static int ravb_probe(struct platform_device *pdev)
netdev_info(ndev, "Base address at %#x, %pM, IRQ %d.\n",
(u32)ndev->base_addr, ndev->dev_addr, ndev->irq);
+ pm_runtime_mark_last_busy(&pdev->dev);
+ pm_runtime_put_autosuspend(&pdev->dev);
+
return 0;
out_napi_del:
@@ -3053,6 +3075,7 @@ static int ravb_probe(struct platform_device *pdev)
pm_runtime_put(&pdev->dev);
out_rpm_disable:
pm_runtime_disable(&pdev->dev);
+ pm_runtime_dont_use_autosuspend(&pdev->dev);
clk_unprepare(priv->refclk);
out_reset_assert:
reset_control_assert(rstc);
@@ -3066,6 +3089,12 @@ static void ravb_remove(struct platform_device *pdev)
struct net_device *ndev = platform_get_drvdata(pdev);
struct ravb_private *priv = netdev_priv(ndev);
const struct ravb_hw_info *info = priv->info;
+ struct device *dev = &priv->pdev->dev;
+ int error;
+
+ error = pm_runtime_resume_and_get(dev);
+ if (error < 0)
+ return;
unregister_netdev(ndev);
if (info->nc_queues)
@@ -3077,8 +3106,9 @@ static void ravb_remove(struct platform_device *pdev)
dma_free_coherent(ndev->dev.parent, priv->desc_bat_size, priv->desc_bat,
priv->desc_bat_dma);
- pm_runtime_put_sync(&pdev->dev);
+ pm_runtime_put_sync_suspend(&pdev->dev);
pm_runtime_disable(&pdev->dev);
+ pm_runtime_dont_use_autosuspend(dev);
clk_unprepare(priv->refclk);
reset_control_assert(priv->rstc);
free_netdev(ndev);
@@ -3160,6 +3190,10 @@ static int ravb_suspend(struct device *dev)
if (ret)
return ret;
+ ret = pm_runtime_force_suspend(&priv->pdev->dev);
+ if (ret)
+ return ret;
+
reset_assert:
return reset_control_assert(priv->rstc);
}
@@ -3182,16 +3216,28 @@ static int ravb_resume(struct device *dev)
ret = ravb_wol_restore(ndev);
if (ret)
return ret;
+ } else {
+ ret = pm_runtime_force_resume(dev);
+ if (ret)
+ return ret;
}
/* Reopening the interface will restore the device to the working state. */
ret = ravb_open(ndev);
if (ret < 0)
- return ret;
+ goto out_rpm_put;
ravb_set_rx_mode(ndev);
netif_device_attach(ndev);
+ return 0;
+
+out_rpm_put:
+ if (!priv->wol_enabled) {
+ pm_runtime_mark_last_busy(dev);
+ pm_runtime_put_autosuspend(dev);
+ }
+
return ret;
}
--
2.39.2
>>> From: Claudiu Beznea <[email protected]>
>>>
>>> Do not apply the RX checksum settings to hardware if the interface is
>>> down.
>>> In case runtime PM is enabled, and while the interface is down, the IP
>>> will be in reset mode (as for some platforms disabling the clocks will
>>> switch the IP to reset mode, which will lead to losing register
>>> contents) and applying settings in reset mode is not an option.
>>> Instead, cache the RX checksum settings and apply them in ravb_open()
>>> through ravb_emac_init().
>>> This has been solved by introducing pm_runtime_active() check. The
>>> device runtime PM usage counter has been incremented to avoid
>>> disabling the device clocks while the check is in progress (if any).
>>>
>>> Commit prepares for the addition of runtime PM.
>>>
>>> Signed-off-by: Claudiu Beznea <[email protected]>
>>
>> Reviewed-by: Sergey Shtylyov <[email protected]>
>
> This will do the same job, without code duplication right?
>
>> static int ravb_set_features(struct net_device *ndev,
>> netdev_features_t features)
>> {
>> struct ravb_private *priv = netdev_priv(ndev);
>> struct device *dev = &priv->pdev->dev;
>> const struct ravb_hw_info *info = priv->info;
>>
>> pm_runtime_get_noresume(dev);
>> if (!pm_runtime_active(dev)) {
>> pm_runtime_put_noidle(dev);
>> ndev->features = features;
>> return 0;
>> }
>>
>> return info->set_feature(ndev, features);
> We now leak the device reference by not calling pm_runtime_put_noidle()
>after this statement...
Oops. So this leak can be fixed like [1]
> The approach seems sane though -- Claudiu, please consider following it.
[1]
static int ravb_set_features(struct net_device *ndev,
netdev_features_t features)
{
struct ravb_private *priv = netdev_priv(ndev);
const struct ravb_hw_info *info = priv->info;
struct device *dev = &priv->pdev->dev;
bool pm_active;
pm_runtime_get_noresume(dev);
pm_active = pm_runtime_active(dev);
pm_runtime_put_noidle(dev);
if (pm_active )
return info->set_feature(ndev, features);
ndev->features = features;
return 0;
}
Hi Sergey,
On Sun, Feb 11, 2024 at 9:40 AM Sergei Shtylyov
<[email protected]> wrote:
>
> On 2/11/24 11:56 AM, Biju Das wrote:
>
> >>>> From: Claudiu Beznea <[email protected]>
> >>>>
> >>>> Do not apply the RX checksum settings to hardware if the interface is
> >>>> down.
> >>>> In case runtime PM is enabled, and while the interface is down, the IP
> >>>> will be in reset mode (as for some platforms disabling the clocks will
> >>>> switch the IP to reset mode, which will lead to losing register
> >>>> contents) and applying settings in reset mode is not an option.
> >>>> Instead, cache the RX checksum settings and apply them in ravb_open()
> >>>> through ravb_emac_init().
> >>>> This has been solved by introducing pm_runtime_active() check. The
> >>>> device runtime PM usage counter has been incremented to avoid
> >>>> disabling the device clocks while the check is in progress (if any).
> >>>>
> >>>> Commit prepares for the addition of runtime PM.
> >>>>
> >>>> Signed-off-by: Claudiu Beznea <[email protected]>
> >>>
> >>> Reviewed-by: Sergey Shtylyov <[email protected]>
> >>
> >> This will do the same job, without code duplication right?
> >>
> >>> static int ravb_set_features(struct net_device *ndev,
> >>> netdev_features_t features)
> >>> {
> >>> struct ravb_private *priv = netdev_priv(ndev);
> >>> struct device *dev = &priv->pdev->dev;
> >>> const struct ravb_hw_info *info = priv->info;
> >>>
> >>> pm_runtime_get_noresume(dev);
> >>> if (!pm_runtime_active(dev)) {
> >>> pm_runtime_put_noidle(dev);
> >>> ndev->features = features;
> >>> return 0;
> >>> }
> >>>
> >>> return info->set_feature(ndev, features);
> >
> >> We now leak the device reference by not calling pm_runtime_put_noidle()
> >> after this statement...
> >
> > Oops. So this leak can be fixed like [1]
> >
> >> The approach seems sane though -- Claudiu, please consider following it.
> >
> > [1]
> > static int ravb_set_features(struct net_device *ndev,
> > netdev_features_t features)
> > {
> > struct ravb_private *priv = netdev_priv(ndev);
> > const struct ravb_hw_info *info = priv->info;
> > struct device *dev = &priv->pdev->dev;
> > bool pm_active;
> >
> > pm_runtime_get_noresume(dev);
> > pm_active = pm_runtime_active(dev);
> > pm_runtime_put_noidle(dev);
>
> There is no point dropping the RPM reference before we access
> the regs...
I don't think there is an issue in accessing register by the usage of
below API's
pm_runtime_get_noresume:--- Bump up runtime PM usage counter of a device.
pm_runtime_active:--- Check whether or not a device is runtime-active.
pm_runtime_put_noidle:--Drop runtime PM usage counter of a device.
Cheers,
Biju
Hi Claudiu,
On Sun, Feb 11, 2024 at 12:13 PM Biju Das <[email protected]> wrote:
>
> Hi Sergey,
>
> On Sun, Feb 11, 2024 at 9:40 AM Sergei Shtylyov
> <[email protected]> wrote:
> >
> > On 2/11/24 11:56 AM, Biju Das wrote:
> >
> > >>>> From: Claudiu Beznea <[email protected]>
> > >>>>
> > >>>> Do not apply the RX checksum settings to hardware if the interface is
> > >>>> down.
Gb eth supports both Rx/Tx Checksum
The intention is not to apply any hardware feature while the interface is done.
So please add a generic commit header and description.
Cheers,
Biju
> > >>>> In case runtime PM is enabled, and while the interface is down, the IP
> > >>>> will be in reset mode (as for some platforms disabling the clocks will
> > >>>> switch the IP to reset mode, which will lead to losing register
> > >>>> contents) and applying settings in reset mode is not an option.
> > >>>> Instead, cache the RX checksum settings and apply them in ravb_open()
> > >>>> through ravb_emac_init().
> > >>>> This has been solved by introducing pm_runtime_active() check. The
> > >>>> device runtime PM usage counter has been incremented to avoid
> > >>>> disabling the device clocks while the check is in progress (if any).
> > >>>>
> > >>>> Commit prepares for the addition of runtime PM.
> > >>>>
> > >>>> Signed-off-by: Claudiu Beznea <[email protected]>
> > >>>
> > >>> Reviewed-by: Sergey Shtylyov <[email protected]>
> > >>
> > >> This will do the same job, without code duplication right?
> > >>
> > >>> static int ravb_set_features(struct net_device *ndev,
> > >>> netdev_features_t features)
> > >>> {
> > >>> struct ravb_private *priv = netdev_priv(ndev);
> > >>> struct device *dev = &priv->pdev->dev;
> > >>> const struct ravb_hw_info *info = priv->info;
> > >>>
> > >>> pm_runtime_get_noresume(dev);
> > >>> if (!pm_runtime_active(dev)) {
> > >>> pm_runtime_put_noidle(dev);
> > >>> ndev->features = features;
> > >>> return 0;
> > >>> }
> > >>>
> > >>> return info->set_feature(ndev, features);
> > >
> > >> We now leak the device reference by not calling pm_runtime_put_noidle()
> > >> after this statement...
> > >
> > > Oops. So this leak can be fixed like [1]
> > >
> > >> The approach seems sane though -- Claudiu, please consider following it.
> > >
> > > [1]
> > > static int ravb_set_features(struct net_device *ndev,
> > > netdev_features_t features)
> > > {
> > > struct ravb_private *priv = netdev_priv(ndev);
> > > const struct ravb_hw_info *info = priv->info;
> > > struct device *dev = &priv->pdev->dev;
> > > bool pm_active;
> > >
> > > pm_runtime_get_noresume(dev);
> > > pm_active = pm_runtime_active(dev);
> > > pm_runtime_put_noidle(dev);
> >
> > There is no point dropping the RPM reference before we access
> > the regs...
>
> I don't think there is an issue in accessing register by the usage of
> below API's
>
> pm_runtime_get_noresume:--- Bump up runtime PM usage counter of a device.
> pm_runtime_active:--- Check whether or not a device is runtime-active.
> pm_runtime_put_noidle:--Drop runtime PM usage counter of a device.
>
> Cheers,
> Biju