[04/10] phy: dphy: Add configuration helpers
diff mbox series

Message ID aa491b814100a670ad16b646765005efbdae05d9.1536138624.git-series.maxime.ripard@bootlin.com
State Superseded
Headers show
Series
  • phy: Add configuration interface for MIPI D-PHY devices
Related show

Commit Message

Maxime Ripard Sept. 5, 2018, 9:16 a.m. UTC
The MIPI D-PHY spec defines default values and boundaries for most of the
parameters it defines. Introduce helpers to help drivers get meaningful
values based on their current parameters, and validate the boundaries of
these parameters if needed.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
---
 drivers/phy/Kconfig               |   8 ++-
 drivers/phy/Makefile              |   1 +-
 drivers/phy/phy-core-mipi-dphy.c  | 160 +++++++++++++++++++++++++++++++-
 include/linux/phy/phy-mipi-dphy.h |   6 +-
 4 files changed, 175 insertions(+)
 create mode 100644 drivers/phy/phy-core-mipi-dphy.c

Comments

Laurent Pinchart Sept. 5, 2018, 1:46 p.m. UTC | #1
Hi Maxime,

Thank you for the patch.

On Wednesday, 5 September 2018 12:16:35 EEST Maxime Ripard wrote:
> The MIPI D-PHY spec defines default values and boundaries for most of the
> parameters it defines. Introduce helpers to help drivers get meaningful
> values based on their current parameters, and validate the boundaries of
> these parameters if needed.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> ---
>  drivers/phy/Kconfig               |   8 ++-
>  drivers/phy/Makefile              |   1 +-
>  drivers/phy/phy-core-mipi-dphy.c  | 160 +++++++++++++++++++++++++++++++-
>  include/linux/phy/phy-mipi-dphy.h |   6 +-
>  4 files changed, 175 insertions(+)
>  create mode 100644 drivers/phy/phy-core-mipi-dphy.c
> 
> diff --git a/drivers/phy/Kconfig b/drivers/phy/Kconfig
> index 5c8d452e35e2..06bd22bd1f4a 100644
> --- a/drivers/phy/Kconfig
> +++ b/drivers/phy/Kconfig
> @@ -15,6 +15,14 @@ config GENERIC_PHY
>  	  phy users can obtain reference to the PHY. All the users of this
>  	  framework should select this config.
> 
> +config GENERIC_PHY_MIPI_DPHY
> +	bool "MIPI D-PHY support"
> +	help
> +	  Generic MIPI D-PHY support.
> +
> +	  Provides a number of helpers a core functions for MIPI D-PHY
> +	  drivers to us.

Do we really need to make this user-selectable ?

>  config PHY_LPC18XX_USB_OTG
>  	tristate "NXP LPC18xx/43xx SoC USB OTG PHY driver"
>  	depends on OF && (ARCH_LPC18XX || COMPILE_TEST)
> diff --git a/drivers/phy/Makefile b/drivers/phy/Makefile
> index 84e3bd9c5665..71c29d2b9af7 100644
> --- a/drivers/phy/Makefile
> +++ b/drivers/phy/Makefile
> @@ -4,6 +4,7 @@
>  #
> 
>  obj-$(CONFIG_GENERIC_PHY)		+= phy-core.o
> +obj-$(CONFIG_GENERIC_PHY_MIPI_DPHY)	+= phy-core-mipi-dphy.o
>  obj-$(CONFIG_PHY_LPC18XX_USB_OTG)	+= phy-lpc18xx-usb-otg.o
>  obj-$(CONFIG_PHY_XGENE)			+= phy-xgene.o
>  obj-$(CONFIG_PHY_PISTACHIO_USB)		+= phy-pistachio-usb.o
> diff --git a/drivers/phy/phy-core-mipi-dphy.c
> b/drivers/phy/phy-core-mipi-dphy.c new file mode 100644
> index 000000000000..6c1ddc7734a2
> --- /dev/null
> +++ b/drivers/phy/phy-core-mipi-dphy.c
> @@ -0,0 +1,160 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2013 NVIDIA Corporation
> + * Copyright (C) 2018 Cadence Design Systems Inc.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/export.h>
> +#include <linux/kernel.h>
> +#include <linux/time64.h>
> +
> +#include <linux/phy/phy.h>
> +#include <linux/phy/phy-mipi-dphy.h>
> +
> +/*
> + * Default D-PHY timings based on MIPI D-PHY specification. Derived from
> the
> + * valid ranges specified in Section 6.9, Table 14, Page 40 of the D-PHY
> + * specification (v1.2) with minor adjustments.

Could you list those adjustments ?

> + */
> +int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
> +				     unsigned int bpp,
> +				     unsigned int lanes,
> +				     struct phy_configure_opts_mipi_dphy *cfg)
> +{
> +	unsigned long hs_clk_rate;
> +	unsigned long ui;
> +
> +	if (!cfg)
> +		return -EINVAL;

Should we really expect cfg to be NULL ?

> +	hs_clk_rate = pixel_clock * bpp / lanes;
> +	ui = DIV_ROUND_UP(NSEC_PER_SEC, hs_clk_rate);
> +
> +	cfg->clk_miss = 0;
> +	cfg->clk_post = 70 + 52 * ui;
> +	cfg->clk_pre = 8;
> +	cfg->clk_prepare = 65;
> +	cfg->clk_settle = 95;
> +	cfg->clk_term_en = 0;
> +	cfg->clk_trail = 80;
> +	cfg->clk_zero = 260;
> +	cfg->d_term_en = 0;
> +	cfg->eot = 0;
> +	cfg->hs_exit = 120;
> +	cfg->hs_prepare = 65 + 5 * ui;
> +	cfg->hs_zero = 145 + 5 * ui;
> +	cfg->hs_settle = 85 + 6 * ui;
> +	cfg->hs_skip = 40;
> +
> +	/*
> +	 * The MIPI D-PHY specification (Section 6.9, v1.2, Table 14, Page 40)
> +	 * contains this formula as:
> +	 *
> +	 *     T_HS-TRAIL = max(n * 8 * ui, 60 + n * 4 * ui)
> +	 *
> +	 * where n = 1 for forward-direction HS mode and n = 4 for reverse-
> +	 * direction HS mode. There's only one setting and this function does
> +	 * not parameterize on anything other that ui, so this code will
> +	 * assumes that reverse-direction HS mode is supported and uses n = 4.
> +	 */
> +	cfg->hs_trail = max(4 * 8 * ui, 60 + 4 * 4 * ui);
> +
> +	cfg->init = 100000;
> +	cfg->lpx = 60;
> +	cfg->ta_get = 5 * cfg->lpx;
> +	cfg->ta_go = 4 * cfg->lpx;
> +	cfg->ta_sure = 2 * cfg->lpx;
> +	cfg->wakeup = 1000000;
> +
> +	cfg->hs_clk_rate = hs_clk_rate;
> +	cfg->lanes = lanes;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(phy_mipi_dphy_get_default_config);
> +
> +/*
> + * Validate D-PHY configuration according to MIPI D-PHY specification
> + * (v1.2, Section Section 6.9 "Global Operation Timing Parameters").
> + */
> +int phy_mipi_dphy_config_validate(struct phy_configure_opts_mipi_dphy *cfg)
> +{
> +	unsigned long ui;
> +
> +	if (!cfg)
> +		return -EINVAL;

Same here.

> +	ui = DIV_ROUND_UP(NSEC_PER_SEC, cfg->hs_clk_rate);
> +
> +	if (cfg->clk_miss > 60)
> +		return -EINVAL;
> +
> +	if (cfg->clk_post < (60 + 52 * ui))
> +		return -EINVAL;
> +
> +	if (cfg->clk_pre < 8)
> +		return -EINVAL;
> +
> +	if (cfg->clk_prepare < 38 || cfg->clk_prepare > 95)
> +		return -EINVAL;
> +
> +	if (cfg->clk_settle < 95 || cfg->clk_settle > 300)
> +		return -EINVAL;
> +
> +	if (cfg->clk_term_en > 38)
> +		return -EINVAL;
> +
> +	if (cfg->clk_trail < 60)
> +		return -EINVAL;
> +
> +	if (cfg->clk_prepare + cfg->clk_zero < 300)
> +		return -EINVAL;
> +
> +	if (cfg->d_term_en > 35 + 4 * ui)
> +		return -EINVAL;
> +
> +	if (cfg->eot > 105 + 12 * ui)
> +		return -EINVAL;
> +
> +	if (cfg->hs_exit < 100)
> +		return -EINVAL;
> +
> +	if (cfg->hs_prepare < 40 + 4 * ui ||
> +	    cfg->hs_prepare > 85 + 6 * ui)
> +		return -EINVAL;
> +
> +	if (cfg->hs_prepare + cfg->hs_zero < 145 + 10 * ui)
> +		return -EINVAL;
> +
> +	if ((cfg->hs_settle < 85 + 6 * ui) ||
> +	    (cfg->hs_settle > 145 + 10 * ui))
> +		return -EINVAL;
> +
> +	if (cfg->hs_skip < 40 || cfg->hs_skip > 55 + 4 * ui)
> +		return -EINVAL;
> +
> +	if (cfg->hs_trail < max(8 * ui, 60 + 4 * ui))
> +		return -EINVAL;
> +
> +	if (cfg->init < 100000)
> +		return -EINVAL;
> +
> +	if (cfg->lpx < 50)
> +		return -EINVAL;
> +
> +	if (cfg->ta_get != 5 * cfg->lpx)
> +		return -EINVAL;
> +
> +	if (cfg->ta_go != 4 * cfg->lpx)
> +		return -EINVAL;
> +
> +	if (cfg->ta_sure < cfg->lpx || cfg->ta_sure > 2 * cfg->lpx)
> +		return -EINVAL;
> +
> +	if (cfg->wakeup < 1000000)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(phy_mipi_dphy_config_validate);
> diff --git a/include/linux/phy/phy-mipi-dphy.h
> b/include/linux/phy/phy-mipi-dphy.h index 792724145290..7656d057198f 100644
> --- a/include/linux/phy/phy-mipi-dphy.h
> +++ b/include/linux/phy/phy-mipi-dphy.h
> @@ -238,4 +238,10 @@ struct phy_configure_opts_mipi_dphy {
>  /* TODO: Add other modes (burst, commands, etc) */
>  #define MIPI_DPHY_MODE_VIDEO_SYNC_PULSE		BIT(0)
> 
> +int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
> +				     unsigned int bpp,
> +				     unsigned int lanes,
> +				     struct phy_configure_opts_mipi_dphy *cfg);
> +int phy_mipi_dphy_config_validate(struct phy_configure_opts_mipi_dphy
> *cfg);
> +
>  #endif /* __PHY_MIPI_DPHY_H_ */
Maxime Ripard Sept. 7, 2018, 1:37 p.m. UTC | #2
On Wed, Sep 05, 2018 at 04:46:05PM +0300, Laurent Pinchart wrote:
> Hi Maxime,
> 
> Thank you for the patch.
> 
> On Wednesday, 5 September 2018 12:16:35 EEST Maxime Ripard wrote:
> > The MIPI D-PHY spec defines default values and boundaries for most of the
> > parameters it defines. Introduce helpers to help drivers get meaningful
> > values based on their current parameters, and validate the boundaries of
> > these parameters if needed.
> > 
> > Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> > ---
> >  drivers/phy/Kconfig               |   8 ++-
> >  drivers/phy/Makefile              |   1 +-
> >  drivers/phy/phy-core-mipi-dphy.c  | 160 +++++++++++++++++++++++++++++++-
> >  include/linux/phy/phy-mipi-dphy.h |   6 +-
> >  4 files changed, 175 insertions(+)
> >  create mode 100644 drivers/phy/phy-core-mipi-dphy.c
> > 
> > diff --git a/drivers/phy/Kconfig b/drivers/phy/Kconfig
> > index 5c8d452e35e2..06bd22bd1f4a 100644
> > --- a/drivers/phy/Kconfig
> > +++ b/drivers/phy/Kconfig
> > @@ -15,6 +15,14 @@ config GENERIC_PHY
> >  	  phy users can obtain reference to the PHY. All the users of this
> >  	  framework should select this config.
> > 
> > +config GENERIC_PHY_MIPI_DPHY
> > +	bool "MIPI D-PHY support"
> > +	help
> > +	  Generic MIPI D-PHY support.
> > +
> > +	  Provides a number of helpers a core functions for MIPI D-PHY
> > +	  drivers to us.
> 
> Do we really need to make this user-selectable ?

Probably not :)

> >  config PHY_LPC18XX_USB_OTG
> >  	tristate "NXP LPC18xx/43xx SoC USB OTG PHY driver"
> >  	depends on OF && (ARCH_LPC18XX || COMPILE_TEST)
> > diff --git a/drivers/phy/Makefile b/drivers/phy/Makefile
> > index 84e3bd9c5665..71c29d2b9af7 100644
> > --- a/drivers/phy/Makefile
> > +++ b/drivers/phy/Makefile
> > @@ -4,6 +4,7 @@
> >  #
> > 
> >  obj-$(CONFIG_GENERIC_PHY)		+= phy-core.o
> > +obj-$(CONFIG_GENERIC_PHY_MIPI_DPHY)	+= phy-core-mipi-dphy.o
> >  obj-$(CONFIG_PHY_LPC18XX_USB_OTG)	+= phy-lpc18xx-usb-otg.o
> >  obj-$(CONFIG_PHY_XGENE)			+= phy-xgene.o
> >  obj-$(CONFIG_PHY_PISTACHIO_USB)		+= phy-pistachio-usb.o
> > diff --git a/drivers/phy/phy-core-mipi-dphy.c
> > b/drivers/phy/phy-core-mipi-dphy.c new file mode 100644
> > index 000000000000..6c1ddc7734a2
> > --- /dev/null
> > +++ b/drivers/phy/phy-core-mipi-dphy.c
> > @@ -0,0 +1,160 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2013 NVIDIA Corporation
> > + * Copyright (C) 2018 Cadence Design Systems Inc.
> > + */
> > +
> > +#include <linux/errno.h>
> > +#include <linux/export.h>
> > +#include <linux/kernel.h>
> > +#include <linux/time64.h>
> > +
> > +#include <linux/phy/phy.h>
> > +#include <linux/phy/phy-mipi-dphy.h>
> > +
> > +/*
> > + * Default D-PHY timings based on MIPI D-PHY specification. Derived from
> > the
> > + * valid ranges specified in Section 6.9, Table 14, Page 40 of the D-PHY
> > + * specification (v1.2) with minor adjustments.
> 
> Could you list those adjustments ?

I will. This was taken from the Tegra DSI driver, so I'm not sure what
these are exactly, but that should be addressed.

> > + */
> > +int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
> > +				     unsigned int bpp,
> > +				     unsigned int lanes,
> > +				     struct phy_configure_opts_mipi_dphy *cfg)
> > +{
> > +	unsigned long hs_clk_rate;
> > +	unsigned long ui;
> > +
> > +	if (!cfg)
> > +		return -EINVAL;
> 
> Should we really expect cfg to be NULL ?

It avoids a kernel panic and it's not in a hot patch, so I'd say yes?

Maxime
Laurent Pinchart Sept. 7, 2018, 2:26 p.m. UTC | #3
Hi Maxime,

On Friday, 7 September 2018 16:37:39 EEST Maxime Ripard wrote:
> On Wed, Sep 05, 2018 at 04:46:05PM +0300, Laurent Pinchart wrote:
> > On Wednesday, 5 September 2018 12:16:35 EEST Maxime Ripard wrote:
> >> The MIPI D-PHY spec defines default values and boundaries for most of
> >> the parameters it defines. Introduce helpers to help drivers get
> >> meaningful values based on their current parameters, and validate the
> >> boundaries of these parameters if needed.
> >> 
> >> Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> >> ---
> >> 
> >>  drivers/phy/Kconfig               |   8 ++-
> >>  drivers/phy/Makefile              |   1 +-
> >>  drivers/phy/phy-core-mipi-dphy.c  | 160 ++++++++++++++++++++++++++++++-
> >>  include/linux/phy/phy-mipi-dphy.h |   6 +-
> >>  4 files changed, 175 insertions(+)
> >>  create mode 100644 drivers/phy/phy-core-mipi-dphy.c

[snip]

> >> diff --git a/drivers/phy/phy-core-mipi-dphy.c
> >> b/drivers/phy/phy-core-mipi-dphy.c new file mode 100644
> >> index 000000000000..6c1ddc7734a2
> >> --- /dev/null
> >> +++ b/drivers/phy/phy-core-mipi-dphy.c
> >> @@ -0,0 +1,160 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +/*
> >> + * Copyright (C) 2013 NVIDIA Corporation
> >> + * Copyright (C) 2018 Cadence Design Systems Inc.
> >> + */
> >> +
> >> +#include <linux/errno.h>
> >> +#include <linux/export.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/time64.h>
> >> +
> >> +#include <linux/phy/phy.h>
> >> +#include <linux/phy/phy-mipi-dphy.h>
> >> +
> >> +/*
> >> + * Default D-PHY timings based on MIPI D-PHY specification. Derived
> >> from the
> >> + * valid ranges specified in Section 6.9, Table 14, Page 40 of the
> >> D-PHY
> >> + * specification (v1.2) with minor adjustments.
> > 
> > Could you list those adjustments ?
> 
> I will. This was taken from the Tegra DSI driver, so I'm not sure what
> these are exactly, but that should be addressed.
> 
> >> + */
> >> +int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
> >> +				     unsigned int bpp,
> >> +				     unsigned int lanes,
> >> +				     struct phy_configure_opts_mipi_dphy *cfg)
> >> +{
> >> +	unsigned long hs_clk_rate;
> >> +	unsigned long ui;
> >> +
> >> +	if (!cfg)
> >> +		return -EINVAL;
> > 
> > Should we really expect cfg to be NULL ?
> 
> It avoids a kernel panic and it's not in a hot patch, so I'd say yes?

A few line below you divide by the lanes parameter without checking whether it 
is equal to 0 first, which would also cause issues.

I believe that invalid values in input parameters should only be handled 
explicitly when considered acceptable for the caller to pass such values. In 
this case a NULL cfg pointer is a bug in the caller, which would get noticed 
during development if the kernel panics.
Maxime Ripard Sept. 10, 2018, 2:16 p.m. UTC | #4
Hi,

On Fri, Sep 07, 2018 at 05:26:29PM +0300, Laurent Pinchart wrote:
> > >> + */
> > >> +int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
> > >> +				     unsigned int bpp,
> > >> +				     unsigned int lanes,
> > >> +				     struct phy_configure_opts_mipi_dphy *cfg)
> > >> +{
> > >> +	unsigned long hs_clk_rate;
> > >> +	unsigned long ui;
> > >> +
> > >> +	if (!cfg)
> > >> +		return -EINVAL;
> > > 
> > > Should we really expect cfg to be NULL ?
> > 
> > It avoids a kernel panic and it's not in a hot patch, so I'd say yes?
> 
> A few line below you divide by the lanes parameter without checking whether it 
> is equal to 0 first, which would also cause issues.

You say that like it would be a bad thing to test for this.

> I believe that invalid values in input parameters should only be handled 
> explicitly when considered acceptable for the caller to pass such values. In 
> this case a NULL cfg pointer is a bug in the caller, which would get noticed 
> during development if the kernel panics.

In the common case, yes. In the case where that pointer is actually
being lost by the caller somewhere down the line and you have to wait
for a while before it happens, then having the driver inoperant
instead of just having a panic seems like the right thing to do.

Maxime
Laurent Pinchart Sept. 10, 2018, 2:28 p.m. UTC | #5
Hi Maxime,

On Monday, 10 September 2018 17:16:03 EEST Maxime Ripard wrote:
> On Fri, Sep 07, 2018 at 05:26:29PM +0300, Laurent Pinchart wrote:
> >>>> + */
> >>>> +int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
> >>>> +				     unsigned int bpp,
> >>>> +				     unsigned int lanes,
> >>>> +				     struct phy_configure_opts_mipi_dphy *cfg)
> >>>> +{
> >>>> +	unsigned long hs_clk_rate;
> >>>> +	unsigned long ui;
> >>>> +
> >>>> +	if (!cfg)
> >>>> +		return -EINVAL;
> >>> 
> >>> Should we really expect cfg to be NULL ?
> >> 
> >> It avoids a kernel panic and it's not in a hot patch, so I'd say yes?
> > 
> > A few line below you divide by the lanes parameter without checking
> > whether it is equal to 0 first, which would also cause issues.
> 
> You say that like it would be a bad thing to test for this.
> 
> > I believe that invalid values in input parameters should only be handled
> > explicitly when considered acceptable for the caller to pass such values.
> > In this case a NULL cfg pointer is a bug in the caller, which would get
> > noticed during development if the kernel panics.
> 
> In the common case, yes. In the case where that pointer is actually
> being lost by the caller somewhere down the line and you have to wait
> for a while before it happens, then having the driver inoperant
> instead of just having a panic seems like the right thing to do.

But why would it happen in the first place ? Why would the pointer be more 
likely here to be NULL than to contain, for instance, an uninitialized value, 
which we don't guard against ?

Patch
diff mbox series

diff --git a/drivers/phy/Kconfig b/drivers/phy/Kconfig
index 5c8d452e35e2..06bd22bd1f4a 100644
--- a/drivers/phy/Kconfig
+++ b/drivers/phy/Kconfig
@@ -15,6 +15,14 @@  config GENERIC_PHY
 	  phy users can obtain reference to the PHY. All the users of this
 	  framework should select this config.
 
+config GENERIC_PHY_MIPI_DPHY
+	bool "MIPI D-PHY support"
+	help
+	  Generic MIPI D-PHY support.
+
+	  Provides a number of helpers a core functions for MIPI D-PHY
+	  drivers to us.
+
 config PHY_LPC18XX_USB_OTG
 	tristate "NXP LPC18xx/43xx SoC USB OTG PHY driver"
 	depends on OF && (ARCH_LPC18XX || COMPILE_TEST)
diff --git a/drivers/phy/Makefile b/drivers/phy/Makefile
index 84e3bd9c5665..71c29d2b9af7 100644
--- a/drivers/phy/Makefile
+++ b/drivers/phy/Makefile
@@ -4,6 +4,7 @@ 
 #
 
 obj-$(CONFIG_GENERIC_PHY)		+= phy-core.o
+obj-$(CONFIG_GENERIC_PHY_MIPI_DPHY)	+= phy-core-mipi-dphy.o
 obj-$(CONFIG_PHY_LPC18XX_USB_OTG)	+= phy-lpc18xx-usb-otg.o
 obj-$(CONFIG_PHY_XGENE)			+= phy-xgene.o
 obj-$(CONFIG_PHY_PISTACHIO_USB)		+= phy-pistachio-usb.o
diff --git a/drivers/phy/phy-core-mipi-dphy.c b/drivers/phy/phy-core-mipi-dphy.c
new file mode 100644
index 000000000000..6c1ddc7734a2
--- /dev/null
+++ b/drivers/phy/phy-core-mipi-dphy.c
@@ -0,0 +1,160 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2013 NVIDIA Corporation
+ * Copyright (C) 2018 Cadence Design Systems Inc.
+ */
+
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/time64.h>
+
+#include <linux/phy/phy.h>
+#include <linux/phy/phy-mipi-dphy.h>
+
+/*
+ * Default D-PHY timings based on MIPI D-PHY specification. Derived from the
+ * valid ranges specified in Section 6.9, Table 14, Page 40 of the D-PHY
+ * specification (v1.2) with minor adjustments.
+ */
+int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
+				     unsigned int bpp,
+				     unsigned int lanes,
+				     struct phy_configure_opts_mipi_dphy *cfg)
+{
+	unsigned long hs_clk_rate;
+	unsigned long ui;
+
+	if (!cfg)
+		return -EINVAL;
+
+	hs_clk_rate = pixel_clock * bpp / lanes;
+	ui = DIV_ROUND_UP(NSEC_PER_SEC, hs_clk_rate);
+
+	cfg->clk_miss = 0;
+	cfg->clk_post = 70 + 52 * ui;
+	cfg->clk_pre = 8;
+	cfg->clk_prepare = 65;
+	cfg->clk_settle = 95;
+	cfg->clk_term_en = 0;
+	cfg->clk_trail = 80;
+	cfg->clk_zero = 260;
+	cfg->d_term_en = 0;
+	cfg->eot = 0;
+	cfg->hs_exit = 120;
+	cfg->hs_prepare = 65 + 5 * ui;
+	cfg->hs_zero = 145 + 5 * ui;
+	cfg->hs_settle = 85 + 6 * ui;
+	cfg->hs_skip = 40;
+
+	/*
+	 * The MIPI D-PHY specification (Section 6.9, v1.2, Table 14, Page 40)
+	 * contains this formula as:
+	 *
+	 *     T_HS-TRAIL = max(n * 8 * ui, 60 + n * 4 * ui)
+	 *
+	 * where n = 1 for forward-direction HS mode and n = 4 for reverse-
+	 * direction HS mode. There's only one setting and this function does
+	 * not parameterize on anything other that ui, so this code will
+	 * assumes that reverse-direction HS mode is supported and uses n = 4.
+	 */
+	cfg->hs_trail = max(4 * 8 * ui, 60 + 4 * 4 * ui);
+
+	cfg->init = 100000;
+	cfg->lpx = 60;
+	cfg->ta_get = 5 * cfg->lpx;
+	cfg->ta_go = 4 * cfg->lpx;
+	cfg->ta_sure = 2 * cfg->lpx;
+	cfg->wakeup = 1000000;
+
+	cfg->hs_clk_rate = hs_clk_rate;
+	cfg->lanes = lanes;
+
+	return 0;
+}
+EXPORT_SYMBOL(phy_mipi_dphy_get_default_config);
+
+/*
+ * Validate D-PHY configuration according to MIPI D-PHY specification
+ * (v1.2, Section Section 6.9 "Global Operation Timing Parameters").
+ */
+int phy_mipi_dphy_config_validate(struct phy_configure_opts_mipi_dphy *cfg)
+{
+	unsigned long ui;
+
+	if (!cfg)
+		return -EINVAL;
+
+	ui = DIV_ROUND_UP(NSEC_PER_SEC, cfg->hs_clk_rate);
+
+	if (cfg->clk_miss > 60)
+		return -EINVAL;
+
+	if (cfg->clk_post < (60 + 52 * ui))
+		return -EINVAL;
+
+	if (cfg->clk_pre < 8)
+		return -EINVAL;
+
+	if (cfg->clk_prepare < 38 || cfg->clk_prepare > 95)
+		return -EINVAL;
+
+	if (cfg->clk_settle < 95 || cfg->clk_settle > 300)
+		return -EINVAL;
+
+	if (cfg->clk_term_en > 38)
+		return -EINVAL;
+
+	if (cfg->clk_trail < 60)
+		return -EINVAL;
+
+	if (cfg->clk_prepare + cfg->clk_zero < 300)
+		return -EINVAL;
+
+	if (cfg->d_term_en > 35 + 4 * ui)
+		return -EINVAL;
+
+	if (cfg->eot > 105 + 12 * ui)
+		return -EINVAL;
+
+	if (cfg->hs_exit < 100)
+		return -EINVAL;
+
+	if (cfg->hs_prepare < 40 + 4 * ui ||
+	    cfg->hs_prepare > 85 + 6 * ui)
+		return -EINVAL;
+
+	if (cfg->hs_prepare + cfg->hs_zero < 145 + 10 * ui)
+		return -EINVAL;
+
+	if ((cfg->hs_settle < 85 + 6 * ui) ||
+	    (cfg->hs_settle > 145 + 10 * ui))
+		return -EINVAL;
+
+	if (cfg->hs_skip < 40 || cfg->hs_skip > 55 + 4 * ui)
+		return -EINVAL;
+
+	if (cfg->hs_trail < max(8 * ui, 60 + 4 * ui))
+		return -EINVAL;
+
+	if (cfg->init < 100000)
+		return -EINVAL;
+
+	if (cfg->lpx < 50)
+		return -EINVAL;
+
+	if (cfg->ta_get != 5 * cfg->lpx)
+		return -EINVAL;
+
+	if (cfg->ta_go != 4 * cfg->lpx)
+		return -EINVAL;
+
+	if (cfg->ta_sure < cfg->lpx || cfg->ta_sure > 2 * cfg->lpx)
+		return -EINVAL;
+
+	if (cfg->wakeup < 1000000)
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL(phy_mipi_dphy_config_validate);
diff --git a/include/linux/phy/phy-mipi-dphy.h b/include/linux/phy/phy-mipi-dphy.h
index 792724145290..7656d057198f 100644
--- a/include/linux/phy/phy-mipi-dphy.h
+++ b/include/linux/phy/phy-mipi-dphy.h
@@ -238,4 +238,10 @@  struct phy_configure_opts_mipi_dphy {
 /* TODO: Add other modes (burst, commands, etc) */
 #define MIPI_DPHY_MODE_VIDEO_SYNC_PULSE		BIT(0)
 
+int phy_mipi_dphy_get_default_config(unsigned long pixel_clock,
+				     unsigned int bpp,
+				     unsigned int lanes,
+				     struct phy_configure_opts_mipi_dphy *cfg);
+int phy_mipi_dphy_config_validate(struct phy_configure_opts_mipi_dphy *cfg);
+
 #endif /* __PHY_MIPI_DPHY_H_ */