linux-kernel - Re: [PATCH v3] treewide: Fix probing of devices in DT overlays

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Message-ID: <20230331101857.wjfwkeiiww4geznk@x260>
Date:   Fri, 31 Mar 2023 13:18:57 +0300
From:   Ivan Bornyakov <i.bornyakov@...rotek.ru>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Wolfram Sang <wsa@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Brown <broonie@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] treewide: Fix probing of devices in DT overlays

On Thu, Mar 30, 2023 at 03:26:13PM +0200, Geert Uytterhoeven wrote:
> When loading a DT overlay that creates a device, the device is not
> probed, unless the DT overlay is unloaded and reloaded again.
> 
> After the recent refactoring to improve fw_devlink, it no longer depends
> on the "compatible" property to identify which device tree nodes will
> become struct devices.   fw_devlink now picks up dangling consumers
> (consumers pointing to descendent device tree nodes of a device that
> aren't converted to child devices) when a device is successfully bound
> to a driver.  See __fw_devlink_pickup_dangling_consumers().
> 
> However, during DT overlay, a device's device tree node can have
> sub-nodes added/removed without unbinding/rebinding the driver.  This
> difference in behavior between the normal device instantiation and
> probing flow vs. the DT overlay flow has a bunch of implications that
> are pointed out elsewhere[1].  One of them is that the fw_devlink logic
> to pick up dangling consumers is never exercised.
> 
> This patch solves the fw_devlink issue by marking all DT nodes added by
> DT overlays with FWNODE_FLAG_NOT_DEVICE (fwnode that won't become
> device), and by clearing the flag when a struct device is actually
> created for the DT node.  This way, fw_devlink knows not to have
> consumers waiting on these newly added DT nodes, and to propagate the
> dependency to an ancestor DT node that has the corresponding struct
> device.
> 
> Based on a patch by Saravana Kannan, which covered only platform and spi
> devices.
> 
> [1] https://lore.kernel.org/r/CAGETcx_bkuFaLCiPrAWCPQz+w79ccDp6=9e881qmK=vx3hBMyg@mail.gmail.com
> 
> Fixes: 4a032827daa89350 ("of: property: Simplify of_link_to_phandle()")
> Link: https://lore.kernel.org/r/CAGETcx_+rhHvaC_HJXGrr5_WAd2+k5f=rWYnkCZ6z5bGX-wj4w@mail.gmail.com
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Acked-by: Mark Brown <broonie@...nel.org>
> Acked-by: Wolfram Sang <wsa@...nel.org> # for I2C

Here is my use-case: a bunch of FPGA-based devices, which are SPI
slaves, WEIM childs and other platform devices, described in DTS with
status = "disabled"; in run-time DT-overlay with status = "okay" for
these devices is loaded via ConfigFS with help of out-of-tree patch.

Although without this patch I had no issues probing overlay-enabled
devices, it won't hurt either.

Tested-by: Ivan Bornyakov <i.bornyakov@...rotek.ru>