Message-ID: <4b844b29-43b1-9e42-6682-678963514766@ti.com>
Date:   Tue, 17 Jan 2023 15:18:46 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     Roger Quadros <rogerq@...nel.org>,
        Leon Romanovsky <leon@...nel.org>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <linux@...linux.org.uk>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <vigneshr@...com>,
        <srk@...com>, <s-vadapalli@...com>
Subject: Re: [PATCH net-next v2] net: ethernet: ti: am65-cpsw/cpts: Fix CPTS
 release action

On 17/01/23 14:57, Roger Quadros wrote:
> Siddharth,
> 
> On 17/01/2023 07:00, 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@...com>
>>>>>> Reviewed-by: Roger Quadros <rogerq@...nel.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@...el.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;
>> 	}
>>
>> ......
>> }
>>
>> Leon,
>>
>> In the above code, when the section corresponding to:
>> dev_info(dev, "cpts disabled\n");
>>
>> is executed, CONFIG_TI_K3_AM65_CPTS is enabled. Therefore, the
>> am65_cpts_release() is not NOP. If the probe fails after the call to
>> am65_cpsw_init_cpts(), then the am65_cpsw_cpts_cleanup() function will be called
>> in the cleanup path of probe, which needs to check for common->cpts not being
>> NULL. This is because common->cpts is NULL after returning 0 from the
>> am65_cpsw_init_cpts() function at the
>> dev_info(dev, "cpts disabled\n");
>>
>> section. Thus, I believe that in this case, am65_cpts_release() shouldn't be
>> invoked from the am65_cpsw_cpts_cleanup() function, since it would have already
>> been invoked from am65_cpts_create()'s cleanup path. This can be ensured by
>> checking whether common->cpts is NULL or not, before invoking
>> am65_cpts_release() within am65_cpsw_cpts_cleanup().
>>
> 
> Yes, I agree.
> 
>>>
>>>> 4. The call to am65_cpts_create() within the am65_cpsw_init_cpts() function
>>>> fails with an error.
>>>
>>> In this case common->cpts is not NULL and will invoke am65_cpts_release() with
>>> invalid handle.
>>
>> Case-4: The call to am65_cpts_create() within the am65_cpsw_init_cpts() function
>> fails with an error. This corresponds to the following section within
>> am65_cpsw_init_cpts():
>>
>> cpts = am65_cpts_create(dev, reg_base, node);
>> if (IS_ERR(cpts)) {
>> ......
>> 	dev_err(dev, "cpts create err %d\n", ret);
>> 	return ret;
>> }
>> 	
>>
>> Roger,
>>
>> If the call to am65_cpts_create() fails with an error other than -EOPNOTSUPP,
>> which corresponds to Case-4, the call to am65_cpts_release() would have been
>> invoked within the am65_cpts_create()'s cleanup path itself if necessary. Also,
>> when the error is not -EOPNOTSUPP, the am65_cpsw_init_cpts() function returns an
>> error, due to which the execution jumps to "err_of_clear" in
>> am65_cpsw_nuss_probe(). Therefore, am65_cpsw_cpts_cleanup() is not invoked in
>> this case, due to which common->cpts being NULL is not a problem.
> 
> Correct.
> 
>>
>>
>> Roger, Leon, please review my comments and let me know. I think that Case-3
>> demands checking whether common->cpts is NULL or not, within the
>> am65_cpsw_cpts_cleanup() function.
> 
> Do you really need a separate am65_cpsw_cpts_cleanup() or can just add
> the NULL check in am65_cpts_release()?

Adding a NULL check in am65_cpts_release() works too. I will implement this in
the v3 patch, if there are no objections to this approach. Leon, please let me
know if this is acceptable.

Regards,
Siddharth.

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