Messages in this thread | | | Date | Fri, 23 Sep 2022 14:32:26 +0200 | Subject | Re: [PATCH v8 3/4] counter: ti-ecap-capture: capture driver support for ECAP | From | Julien Panis <> |
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On 23/09/2022 14:17, Julien Panis wrote: > > > On 23/09/2022 13:35, William Breathitt Gray wrote: >> On Fri, Sep 23, 2022 at 09:23:26AM +0200, Julien Panis wrote: >>> >>> On 23/09/2022 03:08, William Breathitt Gray wrote: >>>> On Thu, Sep 22, 2022 at 07:04:01PM +0200, Julien Panis wrote: >>>>> ECAP hardware on TI AM62x SoC supports capture feature. It can be >>>>> used >>>>> to timestamp events (falling/rising edges) detected on input signal. >>>>> >>>>> This commit adds capture driver support for ECAP hardware on AM62x >>>>> SoC. >>>>> >>>>> In the ECAP hardware, capture pin can also be configured to be in >>>>> PWM mode. Current implementation only supports capture operating >>>>> mode. >>>>> Hardware also supports timebase sync between multiple instances, but >>>>> this driver supports simple independent capture functionality. >>>>> >>>>> Signed-off-by: Julien Panis <jpanis@baylibre.com> >>>> Hello Julien, >>>> >>>> Comments follow inline below. >>>> >>>>> +/** >>>>> + * struct ecap_cnt_dev - device private data structure >>>>> + * @enabled: device state >>>>> + * @clk: device clock >>>>> + * @regmap: device register map >>>>> + * @nb_ovf: number of overflows since capture start >>>>> + * @pm_ctx: device context for PM operations >>>>> + */ >>>>> +struct ecap_cnt_dev { >>>>> + bool enabled; >>>>> + struct clk *clk; >>>>> + struct regmap *regmap; >>>>> + atomic_t nb_ovf; >>>>> + struct { >>>>> + u8 ev_mode; >>>>> + u32 time_cntr; >>>>> + } pm_ctx; >>>>> +}; >>>> Provide documentation for the ev_mode and time_cntr members. You >>>> probably need a lock as well to protect access to this structure or >>>> you'll end up with race problems. >>> Hi William, >>> >>> How can I end up with race problems ? pm_ctx members are only >>> accessed at >>> suspend (after capture/IRQ are disabled) and resume (before >>> capture/IRQ are >>> re-enabled). >>> Is there any risk I did not identify ? >>> >>> Julien >> I was thinking of the ecap_cnt_dev enabled member. The Counter callbacks >> may execute in concurrent threads, so races can appear when you access >> members of the ecap_cnt_dev structure in these callbacks. >> >> Take for example this section of ecap_cnt_enable_write(): >> >> if (enable == ecap_dev->enabled) >> return 0; >> if (enable) >> ecap_cnt_capture_enable(counter); >> else >> ecap_cnt_capture_disable(counter); >> ecap_dev->enabled = enable >> >> Suppose two threads try to enable the count capture. A race condition is >> present where the two threads could see ecap_dev->enabled as false and >> both proceed to call ecap_cnt_capture_enable(). This results in >> pm_runtime_get_sync() bumping the usage count twice and we're left with >> a mismatch the next time ecap_cnt_capture_disable() is called. >> >> William Breathitt Gray > > OK, If I understand well there's the same problem with IO access with > regmap ? > Julien
[ERRATUM] It seems that some spinlock is already used by regmap API. So, only the 'enabled' member needs a lock.
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