by Roger Quadros

[permalink] [raw]

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

Hi,

On 18/01/2023 06:58, Siddharth Vadapalli wrote:
> 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 <[email protected]>
>>>>>>> Reviewed-by: Roger Quadros <[email protected]>
>>>>>>> ---
>>>>>>> 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 <[email protected]> at:
>>>>>>> https://lore.kernel.org/r/[email protected]/
>>>>>>> 2. Collect Reviewed-by tag from Roger Quadros.
>>>>>>>
>>>>>>> v1:
>>>>>>> https://lore.kernel.org/r/[email protected]/
>>>>>>>
>>>>>>> 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.

I couldn't find either.

> 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.

cheers,
-roger