[tpmdd-devel,v2] base/platform: return success when probe function is NULL
diff mbox

Message ID 1448884205-17989-1-git-send-email-martin.wilck@ts.fujitsu.com
State New
Headers show

Commit Message

Martin Wilck Nov. 30, 2015, 11:50 a.m. UTC
From: Martin Wilck <Martin.Wilck@ts.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 may cause problems later for certain usage of platform_driver_register()
and platform_device_register_simple(). I observed a panic while loading
the tpm_tis driver with parameter "force=1" (i.e. registering tpm_tis as
a platform driver), because tpm_tis_init's assumption that the device
returned by platform_device_register_simple() was bound didn't hold any more
(tpmm_chip_alloc() dereferences chip->pdev->driver, causing panic).

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.

v2: fixed style issues, rephrased commit message.

Fixes: b8b2c7d845d5 ("base/platform: assert that dev_pm_domain callbacks are called unconditionally")
Signed-off-by: Martin Wilck <Martin.Wilck@ts.fujitsu.com>
---
 drivers/base/platform.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

Comments

Uwe Kleine-K├Ânig Dec. 1, 2015, 8:30 p.m. UTC | #1
Hello,

On Mon, Nov 30, 2015 at 12:50:05PM +0100, martin.wilck@ts.fujitsu.com wrote:
> From: Martin Wilck <Martin.Wilck@ts.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 may cause problems later for certain usage of platform_driver_register()
> and platform_device_register_simple(). I observed a panic while loading
> the tpm_tis driver with parameter "force=1" (i.e. registering tpm_tis as
> a platform driver), because tpm_tis_init's assumption that the device
> returned by platform_device_register_simple() was bound didn't hold any more
> (tpmm_chip_alloc() dereferences chip->pdev->driver, causing panic).

I'm a bit uncertain if I should be happy with this wording or not. While
b8b2c7d845d5 has a bug which made the tpm_tis driver provoke a panic and
which needs fixing, this doesn't mean that the tpm_tis driver was right.

So "This may cause problems later ..." isn't a correct justification
because even in the presence of the bug introduced by b8b2c7d845d5, the
tpm_tis driver must not assume that it's device is bound on return of
platform_device_register_simple.

It's just that the bug in b8b2c7d845d5 made a wrong assumption of the
tpm_tis driver obvious, and now both need fixing.

If this were my patch, I'd not talk about tpm_tis at all. b8b2c7d845d5
broke binding for platform drivers with no probe function in certain
situations. This is corrected here.

> 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.
> 
> v2: fixed style issues, rephrased commit message.

This must go after the triple-dash below to not be included in the
commit.

> Fixes: b8b2c7d845d5 ("base/platform: assert that dev_pm_domain callbacks are called unconditionally")
> Signed-off-by: Martin Wilck <Martin.Wilck@ts.fujitsu.com>
> ---

Best regards
Uwe

Patch
diff mbox

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) {