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

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Message-ID: <Y8U0Z86y0BnBkRBv@unreal>
Date:   Mon, 16 Jan 2023 13:26:31 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Siddharth Vadapalli <s-vadapalli@...com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        linux@...linux.org.uk, pabeni@...hat.com, rogerq@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, vigneshr@...com, srk@...com
Subject: Re: [PATCH net-next v2] net: ethernet: ti: am65-cpsw/cpts: Fix CPTS
 release action

On Mon, Jan 16, 2023 at 04:07:16PM +0530, Siddharth Vadapalli wrote:
> 
> 
> On 16/01/23 15:34, Leon Romanovsky wrote:
> > On Mon, Jan 16, 2023 at 01:13:36PM +0530, 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:
> >> 1. am65_cpsw_init_cpts() returns 0 since CONFIG_TI_K3_AM65_CPTS is not enabled.
> > 
> > In this case am65_cpsw_cpts_cleanup() will NOP as well.
> > 
> >> 2. am65_cpsw_init_cpts() returns -ENOENT since the cpts node is not defined.
> > 
> > It is an error and all callers unwind properly.
> > 
> >> 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.
> > 
> > It is disabled by CONFIG_TI_K3_AM65_CPTS, which in turn will make
> > am65_cpsw_cpts_cleanup() NOP.
> > 
> >> 4. The call to am65_cpts_create() within the am65_cpsw_init_cpts() function
> >> fails with an error.
> >>
> >> Of the above cases, the am65_cpsw_cpts_cleanup() function would have to handle
> >> cases 1 and 3, since the probe might fail at a later point, following which the
> >> probe cleanup path will invoke the am65_cpts_cpts_cleanup() function. This
> >> function then checks for common->cpts not being NULL, so that it can invoke the
> >> am65_cpts_release() function with this pointer.
> > 
> > I still don't see how it is possible.
> 
> You are right! I apologize for not analyzing the cases well enough. The only
> case where common->cpts will remain NULL and the am65_cpsw_cpts_cleanup()
> function is invoked, is the case where the CONFIG_TI_K3_AM65_CPTS config is
> disabled. As you had pointed it out, in this case, the am65_cpts_release() is
> NOP, so passing the NULL pointer common->cpts will have no effect.
> 
> With this, I understand that the am65_cpsw_cpts_cleanup() function is
> unnecessary like you had mentioned, and am65_cpts_release() can be directly
> invoked for common->cpts. Please let me know if my understanding is correct. If
> so, I will implement this in the v3 patch.

Yes, you understood me right.

Thanks

> 
> Regards,
> Siddharth.