From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E99054D90D8; Tue, 21 Jul 2026 15:16:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784646979; cv=none; b=oVYQsTXorpMx5L0Z4f/nz3S49P6Py1E7mc0hiRZKzsRxBWz6M5evSqM8r2Zjra+5ziNy/RlVs2BE6zyX2XEZ3ghx/4nsZmE3TzVEwARXWWq0GavF5FZKx+bX57yd1SiThmyXglowocH6WWYIlERX75rQxfLI3g1SEvly8DfDL8k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784646979; c=relaxed/simple; bh=uAcT3ywy/2P2x0xh4+d7EzwibNbcjRQIx/4hBThlWIw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ri9gceM1x2ohV4r+UmlSD5CaafhsTkZn2Z89DyZ/ux67M3D+5Fl1Pw5a9KQizrNnI2AXqDzyDUENN0P/bD7ziF8yNQya+ood7P7YaZEAzqzqoiWAICpOHnkFige2TZ5gAO/rhy9Lj8ION7OXAz3FZdMulq5t3qyJs9dNiq+PyvU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=BMIRn54q; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="BMIRn54q" Received: from killaraus.ideasonboard.com (2001-14ba-70f3-e800--a06.rev.dnainternet.fi [IPv6:2001:14ba:70f3:e800::a06]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id BB1DAC1; Tue, 21 Jul 2026 17:15:16 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1784646916; bh=uAcT3ywy/2P2x0xh4+d7EzwibNbcjRQIx/4hBThlWIw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BMIRn54q4P/MHND0CpbZpMup3rUDfEgJJ1qR6IqAZShcWL/J6PSOldWe+qwktfeN9 ySSR1Pgw6JiNp4wikfttzXvb3HfnSRQN5iVbClE0RdYaIQn2Lf45sP09BFKOWy3r3h P+lPfMJowcFwGj4FXFmkQQs60r5//hJgjrARCXiA= Date: Tue, 21 Jul 2026 18:16:14 +0300 From: Laurent Pinchart To: Dave Stevenson Cc: Richard Leitner , Mauro Carvalho Chehab , Sakari Ailus , Hans de Goede , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] media: ov9282: enable single-read I2C transactions Message-ID: <20260721151614.GN50424@killaraus.ideasonboard.com> References: <20260721-cci-single-v1-0-8485171e1393@linux.dev> <20260721-cci-single-v1-2-8485171e1393@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Tue, Jul 21, 2026 at 02:39:46PM +0100, Dave Stevenson wrote: > On Tue, 21 Jul 2026 at 14:25, Richard Leitner wrote: > > > > Some OV9282 camera modules, such as those from Vision Components, fail > > multi-byte register reads with the default CCI I2C regmap access pattern > > and only work when single-register read transactions are used. This > > results in the driver being unable to probe due to a chip id mismatch. > > Those damn stupid Vision Components modules with the MCU that prevents > you reading registers. There's good news, the situation is improving with recent modules. We still have to handle the other ones of course. > I seem to recall Laurent had a plan for how to handle those without > having to patch all the drivers, however I can't find that thread > quickly. I'm thinking of two options: - We can introduce a new standard DT property for I2C device that will be parsed by regmap or the I2C core directly, and switch to single reads. - We could model the MCU as some sort of I2C mux, sitting in DT between the I2C controller and the image sensor, and translate multi-byte reads to single-byte reads in that driver. > > As the driver has no reliable way to identify affected modules enable > > use_single_read for OV9282 unconditionally when creating the CCI regmap. > > > > Tested on an i.M8MP system with OV9282 modules from Vision Components. > > > > Signed-off-by: Richard Leitner > > As regmap does provide a simple way to request this behaviour, and the > only read is the ID register from ov9282_detect, I'll give it an > > Acked-by: Dave Stevenson > > but it's not an ideal situation. Others can debate the alternative > approaches for handling VC modules. > > > --- > > drivers/media/i2c/ov9282.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/media/i2c/ov9282.c b/drivers/media/i2c/ov9282.c > > index 5b6f897a74fcd..8267a0a9c6f2d 100644 > > --- a/drivers/media/i2c/ov9282.c > > +++ b/drivers/media/i2c/ov9282.c > > @@ -1283,6 +1283,11 @@ static int ov9282_probe(struct i2c_client *client) > > struct ov9282 *ov9282; > > int ret; > > > > + const struct cci_regmap_config config = { > > + .reg_addr_bits = 16, > > + .use_single_read = true, > > + }; > > + > > ov9282 = devm_kzalloc(&client->dev, sizeof(*ov9282), GFP_KERNEL); > > if (!ov9282) > > return -ENOMEM; > > @@ -1301,7 +1306,7 @@ static int ov9282_probe(struct i2c_client *client) > > return ret; > > } > > > > - ov9282->regmap = devm_cci_regmap_init_i2c(client, 16); > > + ov9282->regmap = devm_cci_regmap_init_i2c_cfg(client, &config); > > if (IS_ERR(ov9282->regmap)) > > return dev_err_probe(ov9282->dev, PTR_ERR(ov9282->regmap), > > "Failed to init CCI\n"); -- Regards, Laurent Pinchart