nvmem: microchip-otpc: add support

Add support for Microchip OTP controller available on SAMA7G5. The OTPC
controls the access to a non-volatile memory. The memory behind OTPC is
organized into packets, packets are composed by a fixed length header
(4 bytes long) and a variable length payload (payload length is available
in the header). When software request the data at an offset in memory
the OTPC will return (via header + data registers) the whole packet that
has a word at that offset. For the OTP memory layout like below:

offset  OTP Memory layout

         .           .
         .    ...    .
         .           .
0x0E     +-----------+	<--- packet X
         | header  X |
0x12     +-----------+
         | payload X |
0x16     |           |
         |           |
0x1A     |           |
         +-----------+
         .           .
         .    ...    .
         .           .

if user requests data at address 0x16 the data started at 0x0E will be
returned by controller. User will be able to fetch the whole packet
starting at 0x0E (or parts of the packet) via proper registers. The same
packet will be returned if software request the data at offset 0x0E or
0x12 or 0x1A.

The OTP will be populated by Microchip with at least 2 packets first one
being boot configuration packet and the 2nd one being temperature
calibration packet. The packet order will be preserved b/w different chip
revisions but the packet sizes may change.

For the above reasons and to keep the same software able to work on all
chip variants the read function of the driver is working with a packet
id instead of an offset in OTP memory.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20220706100627.6534-3-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 967d0084800e..d72d879a6d34 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -107,6 +107,13 @@ config MTK_EFUSE
 	  This driver can also be built as a module. If so, the module
 	  will be called efuse-mtk.
 
+config MICROCHIP_OTPC
+	tristate "Microchip OTPC support"
+	depends on ARCH_AT91 || COMPILE_TEST
+	help
+	  This driver enable the OTP controller available on Microchip SAMA7G5
+	  SoCs. It controlls the access to the OTP memory connected to it.
+
 config NVMEM_NINTENDO_OTP
 	tristate "Nintendo Wii and Wii U OTP Support"
 	depends on WII || COMPILE_TEST