linux-kernel - Re: [tpmdd-devel] [PATCH v3] base/platform: fix binding for drivers without probe callback

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Date:	Thu, 3 Dec 2015 11:34:58 +0200
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	martin.wilck@...fujitsu.com
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	u.kleine-koenig@...gutronix.de, tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [PATCH v3] base/platform: fix binding for drivers
 without probe callback

On Thu, Dec 03, 2015 at 09:51:44AM +0100, martin.wilck@...fujitsu.com wrote:
> From: Martin Wilck <Martin.Wilck@...fujitsu.com>
> 
> Since b8b2c7d845d5, platform_drv_probe() is called for all platform
> devices. If drv->probe is NULL, and dev_pm_domain_attach() fails,
> platform_drv_probe() will return the error code from dev_pm_domain_attach().
> 
> This causes real_probe() to enter the "probe_failed" path and set
> dev->driver to NULL. Before b8b2c7d845d5, real_probe() would assume
> success if both dev->bus->probe and drv->probe were missing. As a result,
> a device and driver could be "bound" together just by matching their names;
> this doesn't work any more after b8b2c7d845d5.
> 
> This change broke the assumptions of certain drivers; for example, the TPM
> code has long assumed that platform driver and device with matching name
> could be bound in this way. That assumption may cause such drivers to
> fail with Oops during initialization after applying this change. Failure
> in suspend/resume tests under qemu has also been reported.
> 
> This patch restores the previous (4.3.0 and earlier) behavior of
> platform_drv_probe() in the case when the associated platform driver has
> no "probe" function.
> 
> Fixes: b8b2c7d845d5 ("base/platform: assert that dev_pm_domain callbacks are called unconditionally")
> Signed-off-by: Martin Wilck <Martin.Wilck@...fujitsu.com>
> ---
>  v2: fixed style issues, rephrased commit message.
>  v3: rephrased commit message and subject again.
> 
>  drivers/base/platform.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 1dd6d3b..176b59f 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -513,10 +513,15 @@ static int platform_drv_probe(struct device *_dev)
>  		return ret;
>  
>  	ret = dev_pm_domain_attach(_dev, true);
> -	if (ret != -EPROBE_DEFER && drv->probe) {
> -		ret = drv->probe(dev);
> -		if (ret)
> -			dev_pm_domain_detach(_dev, true);
> +	if (ret != -EPROBE_DEFER) {
> +		if (drv->probe) {
> +			ret = drv->probe(dev);
> +			if (ret)
> +				dev_pm_domain_detach(_dev, true);
> +		} else {
> +			/* don't fail if just dev_pm_domain_attach failed */
> +			ret = 0;
> +		}
>  	}
>  
>  	if (drv->prevent_deferred_probe && ret == -EPROBE_DEFER) {
> -- 
> 1.8.3.1

Acked-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

/Jarkko
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