[PATCH v2 1/4] i2c: smbus: Prepare i2c_register_spd for usage on muxed segments

Heiner Kallweit
2024-01-13T11:25:06Z

If this is an adapter on a muxed bus segment, assume that each segment
is connected to a subset of the (> 8) overall memory slots. In this
case let's probe the maximum of 8 slots, however stop if the number
of overall populated slots is reached.

If we're not on a muxed segment and the total number of slots is > 8,
report an error, because then not all SPD eeproms can be addressed.
Presumably the bus is muxed, but the mux config is missing.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
v2:
- remove now obsolete comment
---
drivers/i2c/i2c-smbus.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 74807c6db..44331c5e2 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -309,7 +309,6 @@ EXPORT_SYMBOL_GPL(i2c_free_slave_host_notify_device);
* Restrictions to automatic SPD instantiation:
* - Only works if all filled slots have the same memory type
* - Only works for DDR, DDR2, DDR3 and DDR4 for now
- * - Only works on systems with 1 to 8 memory slots
*/
#if IS_ENABLED(CONFIG_DMI)
void i2c_register_spd(struct i2c_adapter *adap)
@@ -351,13 +350,18 @@ void i2c_register_spd(struct i2c_adapter *adap)
if (!dimm_count)
return;

- dev_info(&adap->dev, "%d/%d memory slots populated (from DMI)\n",
- dimm_count, slot_count);
-
- if (slot_count > 8) {
- dev_warn(&adap->dev,
- "Systems with more than 8 memory slots not supported yet, not instantiating SPD\n");
- return;
+ /* Check whether we're a child adapter on a muxed segment */
+ if (i2c_parent_is_i2c_adapter(adap)) {
+ if (slot_count > 8)
+ slot_count = 8;
+ } else {
+ dev_info(&adap->dev, "%d/%d memory slots populated (from DMI)\n",
+ dimm_count, slot_count);
+ if (slot_count > 8) {
+ dev_err(&adap->dev,
+ "More than 8 memory slots on a single bus, mux config missing?\n");
+ return;
+ }
}

/*
--
2.43.0