linux-kernel - [PATCH v2] check: Add 10bit/slave i2c reg flags support

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Message-ID: <20200527141517.22677-1-Sergey.Semin@baikalelectronics.ru>
Date:   Wed, 27 May 2020 17:15:17 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     <devicetree-compiler@...r.kernel.org>
CC:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Wolfram Sang <wsa@...-dreams.de>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Frank Rowand <frowand.list@...il.com>,
        Rob Herring <robh+dt@...nel.org>, <devicetree@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] check: Add 10bit/slave i2c reg flags support

Recently the I2C-controllers slave interface support was added to the
kernel I2C subsystem. In this case Linux can be used as, for example,
a I2C EEPROM machine. See [1] for details. Other than instantiating
the EEPROM-slave device from user-space there is a way to declare the
device in dts. In this case firstly the I2C bus controller must support
the slave interface. Secondly I2C-slave sub-node of that controller
must have "reg"-property with flag I2C_OWN_SLAVE_ADDRESS set (flag is
declared in [2]). That flag is declared as (1 << 30), which when set
makes dtc unhappy about too big address set for a I2C-slave:

Warning (i2c_bus_reg): /example-2/i2c@...0000/eeprom@64: I2C bus unit address format error, expected "40000064"
Warning (i2c_bus_reg): /example-2/i2c@...0000/eeprom@64:reg: I2C address must be less than 10-bits, got "0x40000064"

Similar problem would have happened if we had set the 10-bit address
flag I2C_TEN_BIT_ADDRESS in the "reg"-property.

In order to fix the problem we suggest to alter the I2C-bus reg-check
algorithm, so one would be aware of the upper bits set. Normally if no
flag specified, the 7-bit address is expected in the "reg"-property.
If I2C_TEN_BIT_ADDRESS is set, then the 10-bit address check will be
performed. The I2C_OWN_SLAVE_ADDRESS flag will be just ignored.

[1] kernel/Documentation/i2c/slave-interface.rst
[2] kernel/include/dt-bindings/i2c/i2c.h

Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Wolfram Sang <wsa@...-dreams.de>
Cc: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Frank Rowand <frowand.list@...il.com>
Cc: Rob Herring <robh+dt@...nel.org>
Cc: devicetree-compiler@...r.kernel.org
Cc: devicetree@...r.kernel.org
Cc: linux-i2c@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

---

Changelog v2:
- Use unsigned numeric literal in the left-shit operation to avoid UB.
---
 checks.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/checks.c b/checks.c
index 4b3c486f1399..7091d1bc38d2 100644
--- a/checks.c
+++ b/checks.c
@@ -1028,6 +1028,7 @@ static void check_i2c_bus_reg(struct check *c, struct dt_info *dti, struct node
 	const char *unitname = get_unitname(node);
 	char unit_addr[17];
 	uint32_t reg = 0;
+	uint32_t addr;
 	int len;
 	cell_t *cells = NULL;
 
@@ -1044,17 +1045,21 @@ static void check_i2c_bus_reg(struct check *c, struct dt_info *dti, struct node
 	}
 
 	reg = fdt32_to_cpu(*cells);
-	snprintf(unit_addr, sizeof(unit_addr), "%x", reg);
+	addr = reg & 0x3FFFFFFFU;
+	snprintf(unit_addr, sizeof(unit_addr), "%x", addr);
 	if (!streq(unitname, unit_addr))
 		FAIL(c, dti, node, "I2C bus unit address format error, expected \"%s\"",
 		     unit_addr);
 
 	for (len = prop->val.len; len > 0; len -= 4) {
 		reg = fdt32_to_cpu(*(cells++));
-		if (reg > 0x3ff)
+		addr = reg & 0x3FFFFFFFU;
+		if ((reg & (1U << 31)) && addr > 0x3ff)
 			FAIL_PROP(c, dti, node, prop, "I2C address must be less than 10-bits, got \"0x%x\"",
-				  reg);
-
+				  addr);
+		else if (!(reg & (1U << 31)) && addr > 0x7f)
+			FAIL_PROP(c, dti, node, prop, "I2C address must be less than 7-bits, got \"0x%x\"",
+				  addr);
 	}
 }
 WARNING(i2c_bus_reg, check_i2c_bus_reg, NULL, &reg_format, &i2c_bus_bridge);
-- 
2.26.2