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 15BF328EB; Mon, 27 Oct 2025 01:11:22 +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=1761527484; cv=none; b=OcWoedfhUb+37rH8e0NM7ImurY8dfmTRfQZACduUGQaZDFLDJIq7GWS269VkHvnDJxUJ6MkQPSDD8yqw9Wbgl+eQGXIJs3YOz8J4ENuq6TFBFZmPlw6xKK4ZoD74J50jJpJsVIGakc6fz+TzNRyp6s6kqX6j6UR6ZPdM3J1hXgQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761527484; c=relaxed/simple; bh=wDAHYZ2XDq9G1bNOJF4J3PL4MjpM9SKkBVwAR7etS9I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TWkjWce6zwBJAEd4HWbXfHgftI+RUxeE43Vefb470KWDJXQ8B71lHzw+2Bs1jlXjhb42E1tDAYK2GU4FibeKJhk89054S/8YvMwWFGp0W3NdRHP7Zo5bcRvc8L8i3/IhlOYG6mRqQdvr8gnKB7kobOwKEkJibAV/1cmfdIiziJY= 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=mjG63zty; 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="mjG63zty" Received: from pendragon.ideasonboard.com (82-203-161-16.bb.dnainternet.fi [82.203.161.16]) by perceval.ideasonboard.com (Postfix) with UTF8SMTPSA id B938B666; Mon, 27 Oct 2025 02:09:29 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1761527370; bh=wDAHYZ2XDq9G1bNOJF4J3PL4MjpM9SKkBVwAR7etS9I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mjG63zty12ng3dohZnH7VMI9WGMBDwHQaQjSBDAlq4Gky9yqB9GNG9u2SonxF/mtV 3XQaQ2mRydgaXAjfrjcsya5qOrE3t6u7KcaOmp4NVv9V68HSi+OcPXTfyYvTvuu+Gl sTKzxc5CSXh5A14ko9mvKra4w1Zy3UG1oE3pGrho= Date: Mon, 27 Oct 2025 03:11:03 +0200 From: Laurent Pinchart To: Frank Li Cc: Marco Felsch , robh@kernel.org, Vinod Koul , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Jiada Wang , dmaengine@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] dmaengine: add device_link support Message-ID: <20251027011103.GR13023@pendragon.ideasonboard.com> References: <20250912-v6-16-topic-dma-devlink-v1-0-4debc2fbf901@pengutronix.de> <20250912-v6-16-topic-dma-devlink-v1-1-4debc2fbf901@pengutronix.de> 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 Thu, Sep 25, 2025 at 12:31:56PM -0400, Frank Li wrote: > On Fri, Sep 12, 2025 at 12:00:41AM +0200, Marco Felsch wrote: > > Shift the device dependency handling to the driver core by adding > > support for devlinks. > > > > The link between the consumer device and the dmaengine device is > > established by the consumer via the dma_request_chan() automatically if > > the dmaengine driver supports it (create_devlink flag set). > > > > By adding the devlink support it is ensured that the supplier can't be > > removed while the consumer still uses the dmaengine. Furthermore it > > ensures that the supplier driver is present and actual bound before the > > consumer is uses the supplier. How is the latter ensured by this patch ? The link is created in dma_request_chan() (which is called by the consumer), after successfully obtaining the channel. I don't see how the link improves that mechanism. > > > > Additional PM and runtime-PM dependency handling can be added easily too > > by setting the required flags (not implemented by this commit). I've long thought that the DMA engine API should offer calls to "prepare" and "unprepare" (names subject to bikeshedding) a DMA engine channel, so that consumers can explicitly indicate when they are getting ready to use DMA, and when they stop. > > > > The new create_devlink flag controlls the devlink creation to not cause > > any regressions with existing dmaengine drivers. This flag can be > > removed once all drivers are successfully tested to support devlinks. > > > > Signed-off-by: Marco Felsch > > --- > > Add previous discussion link: > https://lore.kernel.org/all/aLhUv+mtr1uZTCth@lizhi-Precision-Tower-5810/ > > Another thread > https://lore.kernel.org/dmaengine/20250801120007.GB4906@pendragon.ideasonboard.com/ > > Add Laurent Pinchart, who may instest this topic also. > > Add Rob Herring, who may know why dma engine can't create dev_link default > like other provider (clk, phy, gpio ...) > > > > drivers/dma/dmaengine.c | 15 +++++++++++++++ > > include/linux/dmaengine.h | 3 +++ > > 2 files changed, 18 insertions(+) > > > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c > > index 758fcd0546d8bde8e8dddc6039848feeb1e24475..e81985ab806ae87ff3aa4739fe6f6328b2587f2e 100644 > > --- a/drivers/dma/dmaengine.c > > +++ b/drivers/dma/dmaengine.c > > @@ -858,6 +858,21 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name) > > /* No functional issue if it fails, users are supposed to test before use */ > > #endif > > > > + /* > > + * Devlinks between the dmaengine device and the consumer device > > + * are optional till all dmaengine drivers are converted/tested. > > + */ > > + if (chan->device->create_devlink) { > > + struct device_link *dl; > > + > > + dl = device_link_add(dev, chan->device->dev, DL_FLAG_AUTOREMOVE_CONSUMER); > > I suggest link to per channel device, instead dma engine devices. > chan->dev->device like phy drivers because some dma-engine have per channel > resources, like power domain and clocks. > > Frank > > > + if (!dl) { > > + dev_err(dev, "failed to create device link to %s\n", > > + dev_name(chan->device->dev)); > > + return ERR_PTR(-EINVAL); > > + } > > + } > > + > > chan->name = kasprintf(GFP_KERNEL, "dma:%s", name); > > if (!chan->name) > > return chan; > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h > > index bb146c5ac3e4ccd7bc0afbf3b28e5b3d659ad62f..c67737a358df659f2bf050a9ccb8d23b17ceb357 100644 > > --- a/include/linux/dmaengine.h > > +++ b/include/linux/dmaengine.h > > @@ -817,6 +817,8 @@ struct dma_filter { > > * DMA tansaction with no software intervention for reinitialization. > > * Zero value means unlimited number of entries. > > * @descriptor_reuse: a submitted transfer can be resubmitted after completion > > + * @create_devlink: create a devlink between a dma_chan_dev supplier and > > + * dma-channel consumer device > > * @residue_granularity: granularity of the transfer residue reported > > * by tx_status > > * @device_alloc_chan_resources: allocate resources and return the > > @@ -894,6 +896,7 @@ struct dma_device { > > u32 max_burst; > > u32 max_sg_burst; > > bool descriptor_reuse; > > + bool create_devlink; > > enum dma_residue_granularity residue_granularity; > > > > int (*device_alloc_chan_resources)(struct dma_chan *chan); > > > > -- > > 2.47.3 > > -- Regards, Laurent Pinchart