phy: dphy: Add configuration helpers

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 <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

drivers/phy/Kconfig

···
 	  phy users can obtain reference to the PHY. All the users of this
 	  framework should select this config.
 
+config GENERIC_PHY_MIPI_DPHY
+	bool
+	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)

drivers/phy/Makefile

···
 #
 
 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

drivers/phy/phy-core-mipi-dphy.c

···
+/* 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>
+
+#define PSEC_PER_SEC	1000000000000LL
+
+/*
+ * Minimum D-PHY timings based on MIPI D-PHY specification. Derived
+ * from the valid ranges specified in Section 6.9, Table 14, Page 41
+ * of the D-PHY specification (v2.1).
+ */
+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 long hs_clk_rate;
+	unsigned long long ui;
+
+	if (!cfg)
+		return -EINVAL;
+
+	hs_clk_rate = pixel_clock * bpp;
+	do_div(hs_clk_rate, lanes);
+
+	ui = ALIGN(PSEC_PER_SEC, hs_clk_rate);
+	do_div(ui, hs_clk_rate);
+
+	cfg->clk_miss = 0;
+	cfg->clk_post = 60000 + 52 * ui;
+	cfg->clk_pre = 8000;
+	cfg->clk_prepare = 38000;
+	cfg->clk_settle = 95000;
+	cfg->clk_term_en = 0;
+	cfg->clk_trail = 60000;
+	cfg->clk_zero = 262000;
+	cfg->d_term_en = 0;
+	cfg->eot = 0;
+	cfg->hs_exit = 100000;
+	cfg->hs_prepare = 40000 + 4 * ui;
+	cfg->hs_zero = 105000 + 6 * ui;
+	cfg->hs_settle = 85000 + 6 * ui;
+	cfg->hs_skip = 40000;
+
+	/*
+	 * 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, 60000 + 4 * 4 * ui);
+
+	cfg->init = 100000000;
+	cfg->lpx = 60000;
+	cfg->ta_get = 5 * cfg->lpx;
+	cfg->ta_go = 4 * cfg->lpx;
+	cfg->ta_sure = 2 * cfg->lpx;
+	cfg->wakeup = 1000000000;
+
+	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 long ui;
+
+	if (!cfg)
+		return -EINVAL;
+
+	ui = ALIGN(PSEC_PER_SEC, cfg->hs_clk_rate);
+	do_div(ui, cfg->hs_clk_rate);
+
+	if (cfg->clk_miss > 60000)
+		return -EINVAL;
+
+	if (cfg->clk_post < (60000 + 52 * ui))
+		return -EINVAL;
+
+	if (cfg->clk_pre < 8000)
+		return -EINVAL;
+
+	if (cfg->clk_prepare < 38000 || cfg->clk_prepare > 95000)
+		return -EINVAL;
+
+	if (cfg->clk_settle < 95000 || cfg->clk_settle > 300000)
+		return -EINVAL;
+
+	if (cfg->clk_term_en > 38000)
+		return -EINVAL;
+
+	if (cfg->clk_trail < 60000)
+		return -EINVAL;
+
+	if ((cfg->clk_prepare + cfg->clk_zero) < 300000)
+		return -EINVAL;
+
+	if (cfg->d_term_en > (35000 + 4 * ui))
+		return -EINVAL;
+
+	if (cfg->eot > (105000 + 12 * ui))
+		return -EINVAL;
+
+	if (cfg->hs_exit < 100000)
+		return -EINVAL;
+
+	if (cfg->hs_prepare < (40000 + 4 * ui) ||
+	    cfg->hs_prepare > (85000 + 6 * ui))
+		return -EINVAL;
+
+	if ((cfg->hs_prepare + cfg->hs_zero) < (145000 + 10 * ui))
+		return -EINVAL;
+
+	if ((cfg->hs_settle < (85000 + 6 * ui)) ||
+	    (cfg->hs_settle > (145000 + 10 * ui)))
+		return -EINVAL;
+
+	if (cfg->hs_skip < 40000 || cfg->hs_skip > (55000 + 4 * ui))
+		return -EINVAL;
+
+	if (cfg->hs_trail < max(8 * ui, 60000 + 4 * ui))
+		return -EINVAL;
+
+	if (cfg->init < 100000000)
+		return -EINVAL;
+
+	if (cfg->lpx < 50000)
+		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 < 1000000000)
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL(phy_mipi_dphy_config_validate);

include/linux/phy/phy-mipi-dphy.h

···
 	unsigned char		lanes;
 };
 
+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_ */