linux-kernel - Re: [RFT PATCH v2 2/3] hwmon: (spd5118) Use spd5118 specific read/write operations

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Date: Wed, 19 Jun 2024 02:50:11 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Paul Menzel <pmenzel@...gen.mpg.de>, Armin Wolf <W_Armin@....de>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, linux-kernel@...r.kernel.org, 
	René Rebe <rene@...ctcode.de>, Stephen Horvath <s.horvath@...look.com.au>, 
	Sasha Kozachuk <skozachuk@...gle.com>, John Hamrick <johnham@...gle.com>, 
	Chris Sarra <chrissarra@...gle.com>, linux-hwmon@...r.kernel.org, Jean Delvare <jdelvare@...e.com>, 
	Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [RFT PATCH v2 2/3] hwmon: (spd5118) Use spd5118 specific
 read/write operations

On 2024-06-18 17:23:44+0000, Guenter Roeck wrote:
> On 6/18/24 16:39, Paul Menzel wrote:
> > [Cc: +Heiner]
> > 
> > 
> > Dear Armin,
> > 
> > 
> > Am 19.06.24 um 01:28 schrieb Armin Wolf:
> > > Am 19.06.24 um 00:28 schrieb Wolfram Sang:
> > > 
> > > > > to 86 degrees C. If that doesn't work, we'll be really out of luck
> > > > > with that controller (or at least I don't have an idea what else to try).
> > > > 
> > > > Try CCing Heiner Kallweit for ideas about the i801 controller.
> > 
> > > i am not Heiner Kallweit, but i found something interesting in
> > > commit ba9ad2af7019 ("i2c: i801: Fix I2C Block Read on 8-Series/C220 and later").
> > > 
> > > Basically, it seems that the i802 i2c controller indeed features a SPD write disable bit which blocks all writes for slave addresses 0x50-0x57.
> > > 
> > > Does the i801 i2c controller driver print something like "SPD Write Disable is set" during boot?
> > 
> > Nice find. Yes, it does:
> > 
> 
> Yes, definitely. I didn't have any recent datasheets, so I missed that flag.
> Oh well :-(.
> 
> >      [    5.462605] i801_smbus 0000:00:1f.4: SPD Write Disable is set
> >      [    5.468399] i801_smbus 0000:00:1f.4: SMBus using PCI interrupt
> > 
> 
> Bummer. That explains the problem. It means that the BIOS effectively
> blocks reading the eeprom on your system (because that would require writing
> the page register), as well as changing temperature limits. That is really
> annoying, but there is nothing we can do about it. Maybe the BIOS has a
> configuration flag to enable or disable write protect, but I doubt it.

What about using 16bit addressing mode?

    Alternatively, at initial power on, the host can set the Table 112, “MR11” [3] = ‘1’ to address the entire 1024 bytes of
    non-volatile memory with 2 bytes of address and hence not required to go through page selection to address entire
    non-volatile memory.

regmap-i2c allows 16bit addresses when I2C_FUNC_SMBUS_I2C_BLOCK is supported,
which to me looks like it should be the case on i801 for ICH5.

piix4 doesn't though.

> I'll drop this patch from the series.
> 
> Thanks,
> Guenter
>