crypto: atmel-ecc - add support for ACPI probing on non-AT91 platforms

The Atmel/Microchip EC508A is a I2C device that could be wired into
any platform, and is being used on the Linaro/96boards Secure96
mezzanine adapter. This means it could be found on any platform, even
on ones that use ACPI enumeration (via PRP0001 devices). So update the
code to enable this use case.

This involves tweaking the bus rate discovery code to take ACPI probing
into account, which records the maximum bus rate as a property of the
slave device. For the atmel-ecc code, this means that the effective bus
rate should never exceed the maximum rate, unless we are dealing with
buggy firmware. Nonetheless, let's just use the existing plumbing to
discover the bus rate and keep the existing logic intact.

Signed-off-by: Ard Biesheuvel <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/Kconfig

···
 
 config CRYPTO_DEV_ATMEL_ECC
 	tristate "Support for Microchip / Atmel ECC hw accelerator"
-	depends on ARCH_AT91 || COMPILE_TEST
 	depends on I2C
 	select CRYPTO_ECDH
 	select CRC16

drivers/crypto/atmel-ecc.c

···
 		return -ENODEV;
 	}
 
-	ret = of_property_read_u32(client->adapter->dev.of_node,
-				   "clock-frequency", &bus_clk_rate);
-	if (ret) {
-		dev_err(dev, "of: failed to read clock-frequency property\n");
-		return ret;
+	clk_rate = i2c_acpi_find_bus_speed(&client->adapter->dev);
+	if (!clk_rate) {
+		ret = device_property_read_u32(&client->adapter->dev,
+					       "clock-frequency", &bus_clk_rate);
+		if (ret) {
+			dev_err(dev, "failed to read clock-frequency property\n");
+			return ret;
+		}
 	}
 
 	if (bus_clk_rate > 1000000L) {