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

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

[Heiner Kallweit]

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,
then warn 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:
- Make comments / messages more descriptive
- Remove second patch of the series to ask for testing on lkml
- change dev_err to dev_warn
---
 drivers/i2c/i2c-smbus.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 74807c6db..c45d09782 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -351,13 +351,20 @@ 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;
+	/*
+	 * If we're a child adapter on a muxed segment, then limit slots to 8,
+	 * as this is the max number of SPD EEPROMs that can be addressed per bus.
+	 */
+	if (i2c_parent_is_i2c_adapter(adap)) {
+		slot_count = 8;
+	} else {
+		if (slot_count > 8) {
+			dev_warn(&adap->dev,
+				 "More than 8 memory slots on a single bus, contact i801 maintainer to add missing mux config\n");
+			return;
+		}
+		dev_info(&adap->dev, "%d/%d memory slots populated (from DMI)\n",
+			 dimm_count, slot_count);
 	}
 
 	/*
-- 
2.44.0

Re: [PATCH v2] i2c: smbus: Prepare i2c_register_spd for usage on muxed segments

[Wolfram Sang]

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Hello Heiner,


> +		dev_info(&adap->dev, "%d/%d memory slots populated (from DMI)\n",
> +			 dimm_count, slot_count);

I am still in favor of removing this. I don't like the inconsistency of
the printout depending on the bus being muxed or not. We still have one
printout per device instantiated.

If you agree, I can remove this while applying. If not, then I'll apply
as is. No strong opinion here on my side.

Happy hacking,

   Wolfram


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Re: [PATCH v2] i2c: smbus: Prepare i2c_register_spd for usage on muxed segments

[Heiner Kallweit]

On 04.03.2024 08:46, Wolfram Sang wrote:
> Hello Heiner,
> 
Hello Wolfram,

> 
>> +		dev_info(&adap->dev, "%d/%d memory slots populated (from DMI)\n",
>> +			 dimm_count, slot_count);
> 
> I am still in favor of removing this. I don't like the inconsistency of
> the printout depending on the bus being muxed or not. We still have one
> printout per device instantiated.
> 
> If you agree, I can remove this while applying. If not, then I'll apply
> as is. No strong opinion here on my side.
> 
Yes, please remove it. I'll submit a patch for adding this message to
drivers/firmware/dmi_scan.c. Let's whether DMI maintainers find it useful.

> Happy hacking,
> 
>    Wolfram
> 
Heiner

Re: [PATCH v2] i2c: smbus: Prepare i2c_register_spd for usage on muxed segments

[Wolfram Sang]

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On Sat, Mar 02, 2024 at 09:39:13PM +0100, Heiner Kallweit wrote:
> 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,
> then warn 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>

Removed the printout and applied to for-next, thanks!


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