linux-kernel - Re: [PATCH CFT] usb: ucsi_ccg: Fix command completion handling

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Message-ID: <4c61b43c-1dd0-4f8a-b65f-48752b1cc439@nvidia.com>
Date: Thu, 29 Feb 2024 07:18:44 +0000
From: HaoTien Hsu <haotienh@...dia.com>
To: "Christian A. Ehrhardt" <lk@...e.de>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Heikki
 Krogerus <heikki.krogerus@...ux.intel.com>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, Uwe Kleine-König
	<u.kleine-koenig@...gutronix.de>, Sing-Han Chen <singhanc@...dia.com>,
	Utkarsh Patel <utkarsh.h.patel@...el.com>, Jon Hunter <jonathanh@...dia.com>,
	Wayne Chang <waynec@...dia.com>, WK Tsai <wtsai@...dia.com>
Subject: Re: [PATCH CFT] usb: ucsi_ccg: Fix command completion handling

On 2/15/24 20:03, Christian A. Ehrhardt wrote:
> External email: Use caution opening links or attachments
> 
> 
> Hi Greg,
> 
> On Thu, Feb 15, 2024 at 12:07:20PM +0100, Greg Kroah-Hartman wrote:
>> On Thu, Feb 15, 2024 at 11:10:24AM +0100, Christian A. Ehrhardt wrote:
>>> In case of a spurious or otherwise delayed interrupt
>>> it is possible that CCI still reports the previous completion.
>>> For this reason the UCSI spec provides different completion
>>> bits for normal commands and for UCSI_ACK_CC_CI.
>>>
>>> Only complete a sync command if the correct completion bit
>>> is set.
>>>
>>> This should avoid the need to clear out CCI before starting
>>> a command. Thus remove this code.
>>>
>>> Signed-off-by: Christian A. Ehrhardt <lk@...e.de>
>>> Fixes: e32fd989ac1c ("usb: typec: ucsi: ccg: Move to the new API")
>>
>> What does "CFT" in your subject line mean?
> 
> It's supposed to mean "Call For Testers". More info in the
> "Additional Information" section of the original mail.
> 
> I think the change is necessary and good but I do not have the HW
> to test it.
> 
> I did test a similar change for ucsi_acpi.c that got merged and this
> is the ping for ucsi_ccg.c people that they probably need this, too.
> 
>     regards   Christian
> 
> 

Hi Christian,

If we don't clean the CCI cache in ucsi_ccg_async_write(), there might 
be a potential problem when the driver is polling the results.

In ucsi_init(), we may get EPROBE_DEFER from ucsi_register_port().
Then it does ucsi_reset_ppm() before returning the error code, and we 
will get  UCSI_CCI_RESET_COMPLETE and store it in the CCI cache.
If we don't clean the cache, when the UCSI driver calls ucsi_init() 
again, then in ucsi_reset_ppm(), it will get UCSI_CCI_RESET_COMPLETE 
from the CCI cache instantly.
Then the driver will run the next UCSI commands when the HW is not 
completely reset.

Regards,
Haotien