Re: [PATCH v9 3/4] phy: Add new Exynos USB 2.0 PHY driver

[Kishon Vijay Abraham I]

Hi,

On Thursday 06 March 2014 02:49 PM, Anton Tikhomirov wrote:
> Hi,
>
> > Subject: RE: [PATCH v9 3/4] phy: Add new Exynos USB 2.0 PHY driver
> >
> > Hi,
> >
> > > Subject: Re: [PATCH v9 3/4] phy: Add new Exynos USB 2.0 PHY driver
> > >
> > > Hi,
> > >
> > > On Thursday 06 March 2014 02:22 PM, Anton Tikhomirov wrote:
> > > > Hello,
> > > >
> > > > > Subject: Re: [PATCH v9 3/4] phy: Add new Exynos USB 2.0 PHY driver
> > > > >
> > > > >
> > > > >
> > > > > On Thursday 06 March 2014 01:56 PM, Anton Tikhomirov wrote:
> > > > > > Hi Kamil,
> > > > > >
> > > > > > ...
> > > > > >
> > > > > > > +| 3. Supporting SoCs
> > > > > > > ++--------------------
> > > > > > > +
> > > > > > > +To support a new SoC a new file should be added to the
> > > drivers/phy
> > > > > > > +directory. Each SoC's configuration is stored in an instance of
> > > the
> > > > > > > +struct samsung_usb2_phy_config.
> > > > > > > +
> > > > > > > +struct samsung_usb2_phy_config {
> > > > > > > +	const struct samsung_usb2_common_phy *phys;
> > > > > > > +	unsigned int num_phys;
> > > > > > > +	bool has_mode_switch;
> > > > > >
> > > > > > You missed rate_to_clk here.
> > > > > >
> > > > > > > +};
> > > > > > > +
> > > > > >
> > > > > > ...
> > > > > >
> > > > > > > diff --git a/drivers/phy/phy-samsung-usb2.c b/drivers/phy/phy-
> > > > > samsung-
> > > > > > > usb2.c
> > > > > > > new file mode 100644
> > > > > > > index 0000000..c3b7719
> > > > > > > --- /dev/null
> > > > > > > +++ b/drivers/phy/phy-samsung-usb2.c
> > > > > > > @@ -0,0 +1,222 @@
> > > > > > > +/*
> > > > > > > + * Samsung SoC USB 1.1/2.0 PHY driver
> > > > > > > + *
> > > > > > > + * Copyright (C) 2013 Samsung Electronics Co., Ltd.
> > > > > > > + * Author: Kamil Debski <k.debski@xxxxxxxxxxx>
> > > > > > > + *
> > > > > > > + * This program is free software; you can redistribute it
> > and/or
> > > > > > > modify
> > > > > > > + * it under the terms of the GNU General Public License version
> > 2
> > > > > as
> > > > > > > + * published by the Free Software Foundation.
> > > > > > > + */
> > > > > > > +
> > > > > > > +#include <linux/clk.h>
> > > > > > > +#include <linux/mfd/syscon.h>
> > > > > > > +#include <linux/module.h>
> > > > > > > +#include <linux/of.h>
> > > > > > > +#include <linux/of_address.h>
> > > > > > > +#include <linux/phy/phy.h>
> > > > > > > +#include <linux/platform_device.h>
> > > > > > > +#include <linux/spinlock.h>
> > > > > > > +#include "phy-samsung-usb2.h"
> > > > > > > +
> > > > > > > +static int samsung_usb2_phy_power_on(struct phy *phy)
> > > > > > > +{
> > > > > > > +	struct samsung_usb2_phy_instance *inst =
> > > phy_get_drvdata(phy);
> > > > > > > +	struct samsung_usb2_phy_driver *drv = inst->drv;
> > > > > > > +	int ret;
> > > > > > > +
> > > > > > > +	dev_dbg(drv->dev, "Request to power_on \"%s\" usb phy\n",
> > > > > > > +		inst->cfg->label);
> > > > > > > +	ret = clk_prepare_enable(drv->clk);
> > > > > >
> > > > > > clk_prepare_enable() can sleep, and therefore doesn't allow
> > > > > > samusng_usb2_phy_power_on() to be used in atomic context
> > > > > > (e.g. inside spin_lock-ed area), what sometimes may be desirable.
> > > > > > What about to prepare clock in probe, and just enable it here
> > > > > > (note: clk_enable() doesn't sleep).
> > > > >
> > > > > The PHY power-on callback is anyway called with mutex held, so I
> > > guess
> > > > > it's fine to have clk_prepare_enable() here.
> > > >
> > > > If we rely totally on generic PHY functions such as phy_power_on()
> > > > and friends, why do we need to use locking in callbacks at all.
> > >
> > > Didn't get you.. We don't want to invoke power_on when init is
> > getting
> > > executed or you don't want power on or power off to get executed
> > > simultaneously right? So we need to protect it.
> >
> > I mean callbacks such as samsung_usb2_phy_power_on() which uses
> > spin_lock.
> > It's already protected by mutex in phy_power_on().
>
> Well... phy_power_on() uses mutex to protect power_on() callback.
> power_on() is samsung_usb2_phy_power_on() in our case.
> samsung_usb2_phy_power_on() uses spinlock.
> My question is why do we need to use spinlock _inside_ callback
> if it is already protected by mutex.

It is needed when the same PHY provider implements multiple PHYs. 
phy-core can protect phy-ops of same PHY. However if the PHY provider 
implements multiple PHYs, phy-core won't be able to protect.

Cheers
Kishon
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