Subject: Re: [PATCH] usb: dwc3: Add shutdown to platform_driver

From: Felipe Balbi <[email-masked]>
Date: Wed, 23 Oct 2019 09:31:21 +0300

Hi,

(sorry for the long delay)

Vicente Bergas <[email-masked]> writes:

> On Tuesday, August 27, 2019 2:16:20 PM CEST, Vicente Bergas wrote:
>> On Tuesday, August 27, 2019 1:53:04 PM CEST, Felipe Balbi wrote:
>>> Hi,
>>> 
>>> Vicente Bergas <[email-masked]> writes:
>>>> On Saturday, August 17, 2019 7:41:40 PM CEST, Vicente Bergas wrote:
>>>>> Otherwise the device keeps writing to memory after kexec and disturbs
>>>>> the next kernel.
>> ...
>>> 
>>> why don't you just have shutdown use the same exact function as remove?
>>> Frankly, though, I still don't fully understand what's going wrong
>>> here. Why is the device still alive during kexec?
>>> 
>>> cheers
>>
>> Hi Felipe,
>> the remove and shutdown functions have different prototypes, so
>> shutdown is wrapping remove.
>> Would it be preferable to cast remove as shutdown?
>>
>> The issue with kexec is that the device is being used during the livetime
>> of the first kernel. When the first kernel executes kexec it calls the
>> shutdown function of drivers (instead of remove). Because of this the dwc3
>> device keeps doing things like DMA.
>> While the second kernel is taking over, it gets its memory corrupted with
>> such DMA accesses from the device. When the second kernel reaches the point
>> of taking over the dwc3 device, re-initializes it, but it is already too
>> late. Still worse, if the second kernel did not have the dwc3 driver, it
>> would get endless memory corruptions.
>> All in all, devices that can do DMA need to stop doing it on shutdown.
>>
>> Regards,
>>  Vicenç.
>
> Hi,
> please, can you provide some feedback on this?

I meant something like this:

diff --git a/drivers/usb/dwc3/dwc3-of-simple.c b/drivers/usb/dwc3/dwc3-of-simple.c
index bdac3e7d7b18..e64754be47b4 100644
--- a/drivers/usb/dwc3/dwc3-of-simple.c
+++ b/drivers/usb/dwc3/dwc3-of-simple.c
@@ -110,12 +110,9 @@ static int dwc3_of_simple_probe(struct platform_device *pdev)
 	return ret;
 }
 
-static int dwc3_of_simple_remove(struct platform_device *pdev)
+static void __dwc3_of_simple_teardown(struct dwc3_of_simple *simple)
 {
-	struct dwc3_of_simple	*simple = platform_get_drvdata(pdev);
-	struct device		*dev = &pdev->dev;
-
-	of_platform_depopulate(dev);
+	of_platform_depopulate(simple->dev);
 
 	clk_bulk_disable_unprepare(simple->num_clocks, simple->clks);
 	clk_bulk_put_all(simple->num_clocks, simple->clks);
@@ -126,13 +123,27 @@ static int dwc3_of_simple_remove(struct platform_device *pdev)
 
 	reset_control_put(simple->resets);
 
-	pm_runtime_disable(dev);
-	pm_runtime_put_noidle(dev);
-	pm_runtime_set_suspended(dev);
+	pm_runtime_disable(simple->dev);
+	pm_runtime_put_noidle(simple->dev);
+	pm_runtime_set_suspended(simple->dev);
+}
+
+static int dwc3_of_simple_remove(struct platform_device *pdev)
+{
+	struct dwc3_of_simple	*simple = platform_get_drvdata(pdev);
+
+	__dwc3_of_simple_teardown(simple);
 
 	return 0;
 }
 
+static void dwc3_of_simple_shutdown(struct platform_device *pdev)
+{
+	struct dwc3_of_simple	*simple = platform_get_drvdata(pdev);
+
+	__dwc3_of_simple_teardown(simple);
+}
+
 static int __maybe_unused dwc3_of_simple_runtime_suspend(struct device *dev)
 {
 	struct dwc3_of_simple	*simple = dev_get_drvdata(dev);
@@ -190,6 +201,7 @@ MODULE_DEVICE_TABLE(of, of_dwc3_simple_match);
 static struct platform_driver dwc3_of_simple_driver = {
 	.probe		= dwc3_of_simple_probe,
 	.remove		= dwc3_of_simple_remove,
+	.shutdown	= dwc3_of_simple_shutdown,
 	.driver		= {
 		.name	= "dwc3-of-simple",
 		.of_match_table = of_dwc3_simple_match,

Can you make sure it works as you intended?

-- 
balbi
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