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a="3133288" X-IronPort-AV: E=Sophos;i="6.27,209,1787036400"; d="scan'208";a="3133288" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Nov 2026 00:46:20 -0800 X-CSE-ConnectionGUID: 1U6o/uASRdCC9FMomnfvgQ== X-CSE-MsgGUID: SQGJ+CdBTdy1CT3GmooNkw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,209,1787036400"; d="scan'208";a="9175632" Received: from black.igk.intel.com ([10.91.253.5]) by fmviesa010.fm.intel.com with ESMTP; 12 Nov 2026 00:46:18 -0800 Received: by black.igk.intel.com (Postfix, from userid 1008) id BECD799; Thu, 12 Nov 2026 09:46:16 +0100 (CET) Date: Thu, 12 Nov 2026 09:46:16 +0100 From: Heikki Krogerus To: Atif Ashhar Cc: Mika Westerberg , Andi Shyti , Andy Shevchenko , Jarkko Nikula , Wolfram Sang , linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] i2c: designware: Release slave SCL hold in __i2c_dw_disable() Message-ID: References: <20261104133745.1432212-1-atifashhar@google.com> <20261109102006.GJ176724@black.igk.intel.com> <20261110190559.819337-1-atifashhar@google.com> X-Mailing-List: linux-i2c@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261110190559.819337-1-atifashhar@google.com> Hi guys, On Tue, Nov 10, 2026 at 07:05:59PM +0000, Atif Ashhar wrote: > Hi Mika, > > On Mon, Nov 09, 2026 at 11:20:06AM +0100, Mika Westerberg wrote: > > > + if (tx_hold) { > > > + regmap_read(dev->map, DW_IC_CLR_RD_REQ, &dummy); > > > + regmap_read(dev->map, DW_IC_CLR_TX_ABRT, &dummy); > > > + regmap_write(dev->map, DW_IC_DATA_CMD, 0xFF); > > > > I'm not super familiar with the slave mode so adding Heikki just in case. > > Can this cause some unintended traffic on the bus towards the master? > > No, it cannot initiate new traffic. DW_IC_STATUS_SLAVE_HOLD_TX_FIFO_EMPTY > is only asserted when an external master has already addressed this > controller and initiated a read transfer, and the slave hardware is > actively stretching SCL low waiting for TX data. When no slave read > hold is active, i2c_dw_release_slave_hold() returns early without > writing to DW_IC_DATA_CMD. > > Writing 0xff simply satisfies the ongoing master-clocked read byte > while keeping SDA passively high (released via pull-ups), allowing the > external master to finish clocking the byte and terminate the transfer > with NACK/STOP instead of hanging the bus indefinitely. > > > Also use 0xff instead. > > Ack, I will update 0xFF to 0xff (and wait to see if Heikki has any > comments before sending v2). No comments yet, but just out of curiosity, I'll try to test this. Please go ahead with the v2. I can then give you my Tested-by tag if I figure out how to reproduce the problem fast enough. Thanks, -- heikki