[PATCH 21/40] drm/amdgpu: I2C EEPROM full memory addressing
Luben Tuikov
luben.tuikov at amd.com
Tue Jun 8 21:39:35 UTC 2021
* "eeprom_addr" is now 32-bit wide.
* Remove "slave_addr" from the I2C EEPROM driver
interface. The I2C EEPROM Device Type Identifier
is fixed at 1010b, and the rest of the bits
of the Device Address Byte/Device Select Code,
are memory address bits, where the first three
of those bits are the hardware selection bits.
All this is now a 19-bit address and passed
as "eeprom_addr". This abstracts the I2C bus
for EEPROM devices for this I2C EEPROM driver.
Now clients only pass the 19-bit EEPROM memory
address, to the I2C EEPROM driver, as the 32-bit
"eeprom_addr", from which they want to read from
or write to.
Cc: Jean Delvare <jdelvare at suse.de>
Cc: Alexander Deucher <Alexander.Deucher at amd.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky at amd.com>
Cc: Lijo Lazar <Lijo.Lazar at amd.com>
Cc: Stanley Yang <Stanley.Yang at amd.com>
Cc: Hawking Zhang <Hawking.Zhang at amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov at amd.com>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c | 88 +++++++++++++++++-----
drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.h | 4 +-
2 files changed, 72 insertions(+), 20 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
index 94aeda1c7f8ca0..a5a87affedabf1 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
@@ -24,7 +24,7 @@
#include "amdgpu_eeprom.h"
#include "amdgpu.h"
-/* AT24CM02 has a 256-byte write page size.
+/* AT24CM02 and M24M02-R have a 256-byte write page size.
*/
#define EEPROM_PAGE_BITS 8
#define EEPROM_PAGE_SIZE (1U << EEPROM_PAGE_BITS)
@@ -32,20 +32,72 @@
#define EEPROM_OFFSET_SIZE 2
-static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
- u16 slave_addr, u16 eeprom_addr,
+/* EEPROM memory addresses are 19-bits long, which can
+ * be partitioned into 3, 8, 8 bits, for a total of 19.
+ * The upper 3 bits are sent as part of the 7-bit
+ * "Device Type Identifier"--an I2C concept, which for EEPROM devices
+ * is hard-coded as 1010b, indicating that it is an EEPROM
+ * device--this is the wire format, followed by the upper
+ * 3 bits of the 19-bit address, followed by the direction,
+ * followed by two bytes holding the rest of the 16-bits of
+ * the EEPROM memory address. The format on the wire for EEPROM
+ * devices is: 1010XYZD, A15:A8, A7:A0,
+ * Where D is the direction and sequenced out by the hardware.
+ * Bits XYZ are memory address bits 18, 17 and 16.
+ * These bits are compared to how pins 1-3 of the part are connected,
+ * depending on the size of the part, more on that later.
+ *
+ * Note that of this wire format, a client is in control
+ * of, and needs to specify only XYZ, A15:A8, A7:0, bits,
+ * which is exactly the EEPROM memory address, or offset,
+ * in order to address up to 8 EEPROM devices on the I2C bus.
+ *
+ * For instance, a 2-Mbit I2C EEPROM part, addresses all its bytes,
+ * using an 18-bit address, bit 17 to 0 and thus would use all but one bit of
+ * the 19 bits previously mentioned. The designer would then not connect
+ * pins 1 and 2, and pin 3 usually named "A_2" or "E2", would be connected to
+ * either Vcc or GND. This would allow for up to two 2-Mbit parts on
+ * the same bus, where one would be addressable with bit 18 as 1, and
+ * the other with bit 18 of the address as 0.
+ *
+ * For a 2-Mbit part, bit 18 is usually known as the "Chip Enable" or
+ * "Hardware Address Bit". This bit is compared to the load on pin 3
+ * of the device, described above, and if there is a match, then this
+ * device responds to the command. This way, you can connect two
+ * 2-Mbit EEPROM devices on the same bus, but see one contiguous
+ * memory from 0 to 7FFFFh, where address 0 to 3FFFF is in the device
+ * whose pin 3 is connected to GND, and address 40000 to 7FFFFh is in
+ * the 2nd device, whose pin 3 is connected to Vcc.
+ *
+ * This addressing you encode in the 32-bit "eeprom_addr" below,
+ * namely the 19-bits "XYZ,A15:A0", as a single 19-bit address. For
+ * instance, eeprom_addr = 0x6DA01, is 110_1101_1010_0000_0001, where
+ * XYZ=110b, and A15:A0=DA01h. The XYZ bits become part of the device
+ * address, and the rest of the address bits are sent as the memory
+ * address bytes.
+ *
+ * That is, for an I2C EEPROM driver everything is controlled by
+ * the "eeprom_addr".
+ *
+ * P.S. If you need to write, lock and read the Identification Page,
+ * (M24M02-DR device only, which we do not use), change the "7" to
+ * "0xF" in the macro below, and let the client set bit 20 to 1 in
+ * "eeprom_addr", and set A10 to 0 to write into it, and A10 and A1 to
+ * 1 to lock it permanently.
+ */
+#define MAKE_I2C_ADDR(_aa) ((0xA << 3) | (((_aa) >> 16) & 7))
+
+static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
u8 *eeprom_buf, u16 buf_size, bool read)
{
u8 eeprom_offset_buf[EEPROM_OFFSET_SIZE];
struct i2c_msg msgs[] = {
{
- .addr = slave_addr,
.flags = 0,
.len = EEPROM_OFFSET_SIZE,
.buf = eeprom_offset_buf,
},
{
- .addr = slave_addr,
.flags = read ? I2C_M_RD : 0,
},
};
@@ -58,6 +110,8 @@ static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
buf_size -= len, eeprom_addr += len, eeprom_buf += len) {
/* Set the EEPROM address we want to write to/read from.
*/
+ msgs[0].addr = MAKE_I2C_ADDR(eeprom_addr);
+ msgs[1].addr = msgs[0].addr;
msgs[0].buf[0] = (eeprom_addr >> 8) & 0xff;
msgs[0].buf[1] = eeprom_addr & 0xff;
@@ -71,7 +125,7 @@ static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
* over).
*
* As per the AT24CM02 EEPROM spec, after
- * writing into a page, the I2C driver MUST
+ * writing into a page, the I2C driver should
* terminate the transfer, i.e. in
* "i2c_transfer()" below, with a STOP
* condition, so that the self-timed write
@@ -91,17 +145,20 @@ static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
msgs[1].len = len;
msgs[1].buf = eeprom_buf;
+ /* This constitutes a START-STOP transaction.
+ */
r = i2c_transfer(i2c_adap, msgs, ARRAY_SIZE(msgs));
if (r < ARRAY_SIZE(msgs))
break;
if (!read) {
- /* According to the AT24CM02 EEPROM spec the
- * length of the self-writing cycle, tWR, is
- * 10 ms.
+ /* According to EEPROM specs the length of the
+ * self-writing cycle, tWR (tW), is 10 ms.
*
- * TODO Improve to wait for first ACK for slave address after
- * internal write cycle done.
+ * TODO: Use polling on ACK, aka Acknowledge
+ * Polling, to minimize waiting for the
+ * internal write cycle to complete, as it is
+ * usually smaller than tWR (tW).
*/
msleep(10);
}
@@ -113,7 +170,6 @@ static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
/**
* amdgpu_eeprom_xfer -- Read/write from/to an I2C EEPROM device
* @i2c_adap: pointer to the I2C adapter to use
- * @slave_addr: I2C address of the slave device
* @eeprom_addr: EEPROM address from which to read/write
* @eeprom_buf: pointer to data buffer to read into/write from
* @buf_size: the size of @eeprom_buf
@@ -121,8 +177,7 @@ static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
*
* Returns the number of bytes read/written; -errno on error.
*/
-int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
- u16 slave_addr, u16 eeprom_addr,
+int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
u8 *eeprom_buf, u16 buf_size, bool read)
{
const struct i2c_adapter_quirks *quirks = i2c_adap->quirks;
@@ -136,7 +191,7 @@ int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
limit = quirks->max_write_len;
if (limit == 0) {
- return __amdgpu_eeprom_xfer(i2c_adap, slave_addr, eeprom_addr,
+ return __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
eeprom_buf, buf_size, read);
} else if (limit <= EEPROM_OFFSET_SIZE) {
dev_err_ratelimited(&i2c_adap->dev,
@@ -157,8 +212,7 @@ int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
buf_size -= ps, eeprom_addr += ps, eeprom_buf += ps) {
ps = min(limit, buf_size);
- r = __amdgpu_eeprom_xfer(i2c_adap,
- slave_addr, eeprom_addr,
+ r = __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
eeprom_buf, ps, read);
if (r < 0)
return r;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.h
index 9301e5678910ad..417472be2712e6 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.h
@@ -26,9 +26,7 @@
#include <linux/i2c.h>
-int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap,
- u16 slave_addr, u16 eeprom_addr,
+int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
u8 *eeprom_buf, u16 bytes, bool read);
-
#endif
--
2.32.0
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