Re: [PATCH net-next v2] net: ethernet: ti: am65-cpsw/cpts: Fix CPTS release action

From: Siddharth Vadapalli <s-vadapalli@ti.com>
To: Leon Romanovsky <leon@kernel.org>, Roger Quadros <rogerq@kernel.org>
Cc: <davem@davemloft.net>, <edumazet@google.com>, <kuba@kernel.org>,
	<linux@armlinux.org.uk>, <pabeni@redhat.com>,
	<netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <vigneshr@ti.com>,
	<srk@ti.com>, <s-vadapalli@ti.com>
Subject: Re: [PATCH net-next v2] net: ethernet: ti: am65-cpsw/cpts: Fix CPTS release action
Date: Wed, 18 Jan 2023 10:28:10 +0530	[thread overview]
Message-ID: <7323af1e-1f33-adcf-885e-db604f7a3788@ti.com> (raw)
In-Reply-To: <Y8aHwSnVK9+sAb24@unreal>

On 17/01/23 17:04, Leon Romanovsky wrote:
> On Tue, Jan 17, 2023 at 10:30:26AM +0530, Siddharth Vadapalli wrote:
>> Roger, Leon,
>>
>> On 16/01/23 21:31, Roger Quadros wrote:
>>> Hi Siddharth,
>>>
>>> On 16/01/2023 09:43, Siddharth Vadapalli wrote:
>>>>
>>>>
>>>> On 16/01/23 13:00, Leon Romanovsky wrote:
>>>>> On Mon, Jan 16, 2023 at 10:15:17AM +0530, Siddharth Vadapalli wrote:
>>>>>> The am65_cpts_release() function is registered as a devm_action in the
>>>>>> am65_cpts_create() function in am65-cpts driver. When the am65-cpsw driver
>>>>>> invokes am65_cpts_create(), am65_cpts_release() is added in the set of devm
>>>>>> actions associated with the am65-cpsw driver's device.
>>>>>>
>>>>>> In the event of probe failure or probe deferral, the platform_drv_probe()
>>>>>> function invokes dev_pm_domain_detach() which powers off the CPSW and the
>>>>>> CPSW's CPTS hardware, both of which share the same power domain. Since the
>>>>>> am65_cpts_disable() function invoked by the am65_cpts_release() function
>>>>>> attempts to reset the CPTS hardware by writing to its registers, the CPTS
>>>>>> hardware is assumed to be powered on at this point. However, the hardware
>>>>>> is powered off before the devm actions are executed.
>>>>>>
>>>>>> Fix this by getting rid of the devm action for am65_cpts_release() and
>>>>>> invoking it directly on the cleanup and exit paths.
>>>>>>
>>>>>> Fixes: f6bd59526ca5 ("net: ethernet: ti: introduce am654 common platform time sync driver")
>>>>>> Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
>>>>>> Reviewed-by: Roger Quadros <rogerq@kernel.org>
>>>>>> ---
>>>>>> Changes from v1:
>>>>>> 1. Fix the build issue when "CONFIG_TI_K3_AM65_CPTS" is not set. This
>>>>>>    error was reported by kernel test robot <lkp@intel.com> at:
>>>>>>    https://lore.kernel.org/r/202301142105.lt733Lt3-lkp@intel.com/
>>>>>> 2. Collect Reviewed-by tag from Roger Quadros.
>>>>>>
>>>>>> v1:
>>>>>> https://lore.kernel.org/r/20230113104816.132815-1-s-vadapalli@ti.com/
>>>>>>
>>>>>>  drivers/net/ethernet/ti/am65-cpsw-nuss.c |  8 ++++++++
>>>>>>  drivers/net/ethernet/ti/am65-cpts.c      | 15 +++++----------
>>>>>>  drivers/net/ethernet/ti/am65-cpts.h      |  5 +++++
>>>>>>  3 files changed, 18 insertions(+), 10 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
>>>>>> index 5cac98284184..00f25d8a026b 100644
>>>>>> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
>>>>>> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
>>>>>> @@ -1913,6 +1913,12 @@ static int am65_cpsw_am654_get_efuse_macid(struct device_node *of_node,
>>>>>>  	return 0;
>>>>>>  }
>>>>>>  
>>>>>> +static void am65_cpsw_cpts_cleanup(struct am65_cpsw_common *common)
>>>>>> +{
>>>>>> +	if (IS_ENABLED(CONFIG_TI_K3_AM65_CPTS) && common->cpts)
>>>>>
>>>>> Why do you have IS_ENABLED(CONFIG_TI_K3_AM65_CPTS), if
>>>>> am65_cpts_release() defined as empty when CONFIG_TI_K3_AM65_CPTS not set?
>>>>>
>>>>> How is it possible to have common->cpts == NULL?
>>>>
>>>> Thank you for reviewing the patch. I realize now that checking
>>>> CONFIG_TI_K3_AM65_CPTS is unnecessary.
>>>>
>>>> common->cpts remains NULL in the following cases:
>>
>> I realized that the cases I mentioned are not explained clearly. Therefore, I
>> will mention the cases again, along with the section of code they correspond to,
>> in order to make it clear.
>>
>> Case-1: am65_cpsw_init_cpts() returns 0 since CONFIG_TI_K3_AM65_CPTS is not
>> enabled. This corresponds to the following section within am65_cpsw_init_cpts():
>>
>> if (!IS_ENABLED(CONFIG_TI_K3_AM65_CPTS))
>> 	return 0;
>>
>> In this case, common->cpts remains NULL, but it is not a problem even if the
>> am65_cpsw_nuss_probe() fails later, since the am65_cpts_release() function is
>> NOP. Thus, this case is not an issue.
>>
>> Case-2: am65_cpsw_init_cpts() returns -ENOENT since the cpts node is not present
>> in the device tree. This corresponds to the following section within
>> am65_cpsw_init_cpts():
>>
>> node = of_get_child_by_name(dev->of_node, "cpts");
>> if (!node) {
>> 	dev_err(dev, "%s cpts not found\n", __func__);
>> 	return -ENOENT;
>> }
>>
>> In this case as well, common->cpts remains NULL, but it is not a problem because
>> the probe fails and the execution jumps to "err_of_clear", which doesn't invoke
>> am65_cpsw_cpts_cleanup(). Therefore, common->cpts being NULL is not a problem.
>>
>> Case-3 and Case-4 are described later in this mail.
>>
>>>> 1. am65_cpsw_init_cpts() returns 0 since CONFIG_TI_K3_AM65_CPTS is not enabled.
>>>> 2. am65_cpsw_init_cpts() returns -ENOENT since the cpts node is not defined.
>>>> 3. The call to am65_cpts_create() fails within the am65_cpsw_init_cpts()
>>>> function with a return value of 0 when cpts is disabled.
>>>
>>> In this case common->cpts is not NULL and is set to error pointer.
>>> Probe will continue normally.
>>> Is it OK to call any of the cpts APIs with invalid handle?
>>> Also am65_cpts_release() will be called with invalid handle.
>>
>> Yes Roger, thank you for pointing it out. When I wrote "cpts is disabled", I had
>> meant that the following section is executed within the am65_cpsw_init_cpts()
>> function:
>>
>> Case-3:
>>
>> cpts = am65_cpts_create(dev, reg_base, node);
>> if (IS_ERR(cpts)) {
>> 	int ret = PTR_ERR(cpts);
>>
>> 	of_node_put(node);
>> 	if (ret == -EOPNOTSUPP) {
>> 		dev_info(dev, "cpts disabled\n");
>> 		return 0;
>> 	}
> 
> This code block is unreachable, because of config earlier.
>   1916 static int am65_cpsw_init_cpts(struct am65_cpsw_common *common)
>   1917 {
> ...
>   1923         if (!IS_ENABLED(CONFIG_TI_K3_AM65_CPTS))
>   1924                 return 0;
> ...
>   1933         cpts = am65_cpts_create(dev, reg_base, node);
>   1934         if (IS_ERR(cpts)) {
>   1935                 int ret = PTR_ERR(cpts);
>   1936
>   1937                 of_node_put(node);
>   1938                 if (ret == -EOPNOTSUPP) {
>   1939                         dev_info(dev, "cpts disabled\n");
>   1940                         return 0;
>   1941                 }
> 
> You should delete all the logic above.

Leon,

I did not realize that the code block is unreachable. I had assumed it was valid
and handled the case where the CONFIG_TI_K3_AM65_CPTS config is enabled and one
of the functions within am65_cpts_create() return -EOPNOTSUPP, since this
section of code was already present. I analyzed the possible return values of
all the functions within am65_cpts_create() and like you pointed out, none of
them seem to return -EOPNOTSUPP.

Roger,

Please let me know if you can identify a case where CONFIG_TI_K3_AM65_CPTS is
enabled and one of the functions within the am65_cpts_create() function return
-EOPNOTSUPP. I was unable to find one after analyzing the return values.
Therefore, I shall proceed with adding a cleanup patch which deletes the
unreachable code block, followed by updating this patch with Leon's first
suggestion of dropping am65_cpsw_cpts_cleanup() entirely, since common->cpts
being NULL won't have any problem and am65_cpts_release() can be invoked
directly. I will post these two patches as the v3 series if there are no issues.

Regards,
Siddharth.