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Date:   Wed, 31 Aug 2022 21:21:29 +0100
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Isaac J. Manjarres" <isaacmanjarres@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        stable@vger.kernel.org, Saravana Kannan <saravanak@google.com>,
        Guenter Roeck <linux@roeck-us.net>, kernel-team@android.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] driver core: Don't probe devices after
 bus_type.match() probe deferral
Message-ID: <Yw/CyRFr1bYNlNGh@shell.armlinux.org.uk>
References: <20220817184026.3468620-1-isaacmanjarres@google.com>
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In-Reply-To: <20220817184026.3468620-1-isaacmanjarres@google.com>
Sender: Russell King (Oracle) <linux@armlinux.org.uk>
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Greg,

Are you happy for me to pick up this patch as part of the fixes for the
AMBA changes? The original patch that it is fixing is a patch that was
part of a series that was merged through my tree.

It's fixing a problem that has been noticed by several people and the
fix is now a few weeks old.

Thanks.

On Wed, Aug 17, 2022 at 11:40:26AM -0700, Isaac J. Manjarres wrote:
> Both __device_attach_driver() and __driver_attach() check the return
> code of the bus_type.match() function to see if the device needs to be
> added to the deferred probe list. After adding the device to the list,
> the logic attempts to bind the device to the driver anyway, as if the
> device had matched with the driver, which is not correct.
> 
> If __device_attach_driver() detects that the device in question is not
> ready to match with a driver on the bus, then it doesn't make sense for
> the device to attempt to bind with the current driver or continue
> attempting to match with any of the other drivers on the bus. So, update
> the logic in __device_attach_driver() to reflect this.
> 
> If __driver_attach() detects that a driver tried to match with a device
> that is not ready to match yet, then the driver should not attempt to bind
> with the device. However, the driver can still attempt to match and bind
> with other devices on the bus, as drivers can be bound to multiple
> devices. So, update the logic in __driver_attach() to reflect this.
> 
> Cc: stable@vger.kernel.org
> Cc: Saravana Kannan <saravanak@google.com>
> Fixes: 656b8035b0ee ("ARM: 8524/1: driver cohandle -EPROBE_DEFER from bus_type.match()")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
> Reviewed-by: Saravana Kannan <saravanak@google.com>
> ---
>  drivers/base/dd.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> v1 -> v2:
> - Fixed the logic in __driver_attach() to allow a driver to continue
>   attempting to match and bind with devices in case of any error, not
>   just probe deferral.
> 
> v2 -> v3:
> - Restored the patch back to v1.
> - Added Guenter's Tested-by tag.
> - Added Saravana's Reviewed-by tag.
> - Cc'd stable@vger.kernel.org
> 
> Greg,
> 
> This is the final version of this patch. Can you please pick this up?
> 
> Thanks,
> Isaac
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 70f79fc71539..90b31fb141a5 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -881,6 +881,11 @@ static int __device_attach_driver(struct device_driver *drv, void *_data)
>  		dev_dbg(dev, "Device match requests probe deferral\n");
>  		dev->can_match = true;
>  		driver_deferred_probe_add(dev);
> +		/*
> +		 * Device can't match with a driver right now, so don't attempt
> +		 * to match or bind with other drivers on the bus.
> +		 */
> +		return ret;
>  	} else if (ret < 0) {
>  		dev_dbg(dev, "Bus failed to match device: %d\n", ret);
>  		return ret;
> @@ -1120,6 +1125,11 @@ static int __driver_attach(struct device *dev, void *data)
>  		dev_dbg(dev, "Device match requests probe deferral\n");
>  		dev->can_match = true;
>  		driver_deferred_probe_add(dev);
> +		/*
> +		 * Driver could not match with device, but may match with
> +		 * another device on the bus.
> +		 */
> +		return 0;
>  	} else if (ret < 0) {
>  		dev_dbg(dev, "Bus failed to match device: %d\n", ret);
>  		return ret;
> -- 
> 2.37.1.595.g718a3a8f04-goog
> 
> 

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