RE: [EXTERNAL] Re: [PATCH v2] i2c: designware: Enable SAR in slave mode for Multiple SAR controllers

[Umesh Kumar]

Hi Andy , 

It's not a Marvell-custom bit — it's the Synopsys DW_apb_i2c IC_ENABLE.SAR_EN field (bit 19), 
part of the Multiple SAR feature described in the DataBook. I'll add the DataBook reference to 
both the commit message and the code comment in v3.

Regards ,
Umesh Kumar

From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> 
Sent: Wednesday, August 12, 2026 12:46 PM
To: Umesh Kumar <ukumar@xxxxxxxxxxx>
Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>; Andi Shyti <andi.shyti@xxxxxxxxxx>; Bharat Bhushan <bbhushan2@xxxxxxxxxxx>; linux-i2c@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: [EXTERNAL] Re: [PATCH v2] i2c: designware: Enable SAR in slave mode for Multiple SAR controllers

On Wed, Aug 12, 2026 at 09: 10: 17AM +0530, Umesh Kumar wrote: > DesignWare controllers synthesised with the Multiple SAR feature (e. g. > Marvell CN20K) only acknowledge traffic to the primary slave address > (IC_SAR) when IC_ENABLE[19]
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On Wed, Aug 12, 2026 at 09:10:17AM +0530, Umesh Kumar wrote:
> DesignWare controllers synthesised with the Multiple SAR feature (e.g.
> Marvell CN20K) only acknowledge traffic to the primary slave address
> (IC_SAR) when IC_ENABLE[19] (SAR_EN) is set. The slave enable path
> writes only IC_ENABLE[0], so on such controllers the target never ACKs
> its address and a remote master cannot reach it.
> 
> Set SAR_EN together with ENABLE when entering slave mode. The bit is
> reserved (and ignored) on single-SAR controllers, so existing users are
> unaffected.

In the commit message and in the code comment below, can we refer to Synopsys
DataBook for I²C where this bit is described? Or is it Marvell custom bit?

-- 
With Best Regards,
Andy Shevchenko