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Date: Thu, 27 Jun 2024 17:49:53 +0200
From: Fabrice Gasnier <fabrice.gasnier@...s.st.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Greg Kroah-Hartman
<gregkh@...uxfoundation.org>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Neil Armstrong
<neil.armstrong@...aro.org>,
<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
Nikita Travkin <nikita@...n.ru>,
<linux-stm32@...md-mailman.stormreply.com>,
<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Linux-stm32] [PATCH v2 6/7] usb: typec: ucsi: extract common
code for command handling
On 6/25/24 18:49, Dmitry Baryshkov wrote:
> On Tue, Jun 25, 2024 at 05:24:54PM GMT, Fabrice Gasnier wrote:
>> On 6/21/24 00:55, Dmitry Baryshkov wrote:
>>> Extract common functions to handle command sending and to handle events
>>> from UCSI. This ensures that all UCSI glue drivers handle the ACKs in
>>> the same way.
>>>
>>> The CCG driver used DEV_CMD_PENDING both for internal
>>> firmware-related commands and for UCSI control handling. Leave the
>>> former use case intact.
>>>
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>> ---
>>> drivers/usb/typec/ucsi/ucsi.c | 43 +++++++++++++++++++++++++++
>>> drivers/usb/typec/ucsi/ucsi.h | 7 +++++
>>> drivers/usb/typec/ucsi/ucsi_acpi.c | 46 ++---------------------------
>>> drivers/usb/typec/ucsi/ucsi_ccg.c | 21 ++-----------
>>> drivers/usb/typec/ucsi/ucsi_glink.c | 47 ++---------------------------
>>> drivers/usb/typec/ucsi/ucsi_stm32g0.c | 44 ++--------------------------
>>> drivers/usb/typec/ucsi/ucsi_yoga_c630.c | 52 ++-------------------------------
>>> 7 files changed, 62 insertions(+), 198 deletions(-)
>>>
>>> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
>>> index 4ba22323dbf9..691ee0c4ef87 100644
>>> --- a/drivers/usb/typec/ucsi/ucsi.c
>>> +++ b/drivers/usb/typec/ucsi/ucsi.c
>>> @@ -36,6 +36,48 @@
>>> */
>>> #define UCSI_SWAP_TIMEOUT_MS 5000
>>>
>>> +void ucsi_notify_common(struct ucsi *ucsi, u32 cci)
>>> +{
>>> + if (UCSI_CCI_CONNECTOR(cci))
>>> + ucsi_connector_change(ucsi, UCSI_CCI_CONNECTOR(cci));
>>> +
>>> + if (cci & UCSI_CCI_ACK_COMPLETE &&
>>> + test_bit(ACK_PENDING, &ucsi->flags))
>>> + complete(&ucsi->complete);
>>> +
>>> + if (cci & UCSI_CCI_COMMAND_COMPLETE &&
>>> + test_bit(COMMAND_PENDING, &ucsi->flags))
>>> + complete(&ucsi->complete);
>>
>> Hi Dmitry,
>>
>> I've recently faced some race with ucsi_stm32g0 driver, and have sent a
>> fix for it [1], as you've noticed in the cover letter.
>>
>> To fix that, I've used test_and_clear_bit() in above two cases, instead
>> of test_bit().
>
> Could you possible describe, why do you need test_and_clear_bit()
> instead of just test_bit()? The bits are cleared at the end of the
> .sync_write(), also there can be no other command (or ACK_CC) submission
> before this one is fully processed.
Hi Dmitry,
It took me some time to reproduce this race I observed earlier.
(I observe this during DR swap.)
Once the ->async_control(UCSI_ACK_CC_CI) call bellow gets completed, and
before the ACK_PENDING bit gets cleared, e.g. clear_bit(ACK_PENDING), I
get an asynchronous interrupt.
Basically, Then the above complete() gets called (due to
UCSI_CCI_ACK_COMPLETE & ACK_PENDING).
Subsequent UCSI_GET_CONNECTOR_STATUS command (from
ucsi_handle_connector_change) will be unblocked immediately due to
complete() call has already happen, without UCSI_CCI_COMMAND_COMPLETE
cci flag, hence returning -EIO.
This is where the test_and_clear_bit() atomic operation helps, to avoid
non atomic operation:
-> async_control(UCSI_ACK_CC_CI)
new interrupt may occur here
-> clear_bit(ACK_PENDING)
>
>>
>> https://lore.kernel.org/linux-usb/20240612124656.2305603-1-fabrice.gasnier@foss.st.com/
>>
>>> +}
>>> +EXPORT_SYMBOL_GPL(ucsi_notify_common);
>>> +
>>> +int ucsi_sync_control_common(struct ucsi *ucsi, u64 command)
>>> +{
>>> + bool ack = UCSI_COMMAND(command) == UCSI_ACK_CC_CI;
>>> + int ret;
>>> +
>>> + if (ack)
>>> + set_bit(ACK_PENDING, &ucsi->flags);
>>> + else
>>> + set_bit(COMMAND_PENDING, &ucsi->flags);
>>> +
>>> + ret = ucsi->ops->async_control(ucsi, command);
>>> + if (ret)
>>> + goto out_clear_bit;
>>> +
>>> + if (!wait_for_completion_timeout(&ucsi->complete, 5 * HZ))
>>> + ret = -ETIMEDOUT;
>>
>> With test_and_clear_bit(), could return 0, in case of success here.
>
> Oh, I see. So your code returns earlier. I have a feeling that this
> approach is less logical and slightly harder to follow.
By reading your proposal bellow, I'd agree with you.
>
> Maybe it's easier if it is implemented as:
>
> if (wait_for_completion_timeout(...))
> return 0;
Yes, sounds good to me.
>
> if (ack)
> clear_bit(ACK_PENDING)
> else
> clear_bit(COMMAND_PENDING)
>
> return -ETIMEDOUT;
>
>
> OR
>
> if (!wait_for_completion_timeout(...)) {
> if (ack)
> clear_bit(ACK_PENDING)
> else
> clear_bit(COMMAND_PENDING)
>
> return -ETIMEDOUT;
> }
Both seems fine.
Please advise,
BR,
Fabrice
>
> return 0;
>
> But really, unless there is an actual issue with the current code, I'd
> prefer to keep it. It makes it clear that the bits are set and then are
> cleared properly.
>
>> I'd suggest to use similar approach here, unless you see some drawback?
>>
>> Best Regards,
>> Fabrice
>>
>>> +
>>> +out_clear_bit:
>>> + if (ack)
>>> + clear_bit(ACK_PENDING, &ucsi->flags);
>>> + else
>>> + clear_bit(COMMAND_PENDING, &ucsi->flags);
>>> +
>>> + return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(ucsi_sync_control_common);
>>> +
>>> static int ucsi_acknowledge(struct ucsi *ucsi, bool conn_ack)
>>> {
>>> u64 ctrl;
>>> @@ -1883,6 +1925,7 @@ struct ucsi *ucsi_create(struct device *dev, const struct ucsi_operations *ops)
>>> INIT_WORK(&ucsi->resume_work, ucsi_resume_work);
>>> INIT_DELAYED_WORK(&ucsi->work, ucsi_init_work);
>>> mutex_init(&ucsi->ppm_lock);
>>> + init_completion(&ucsi->complete);
>>> ucsi->dev = dev;
>>> ucsi->ops = ops;
>>
>> [snip]
>>
>>> ucsi->ucsi = ucsi_create(dev, &pmic_glink_ucsi_ops);
>>> diff --git a/drivers/usb/typec/ucsi/ucsi_stm32g0.c b/drivers/usb/typec/ucsi/ucsi_stm32g0.c
>>> index 14737ca3724c..d948c3f579e1 100644
>>> --- a/drivers/usb/typec/ucsi/ucsi_stm32g0.c
>>> +++ b/drivers/usb/typec/ucsi/ucsi_stm32g0.c
>>> @@ -61,11 +61,7 @@ struct ucsi_stm32g0 {
>>
>> [snip]
>>
>>> -
>>> - ret = ucsi_stm32g0_async_control(ucsi, command);
>>> - if (ret)
>>> - goto out_clear_bit;
>>> -
>>> - if (!wait_for_completion_timeout(&g0->complete, msecs_to_jiffies(5000)))
>>> - ret = -ETIMEDOUT;
>>> - else
>>> - return 0;
>>> -
>>> -out_clear_bit:
>>> - if (ack)
>>> - clear_bit(ACK_PENDING, &g0->flags);
>>> - else
>>> - clear_bit(COMMAND_PENDING, &g0->flags);
>>> -
>>> - return ret;
>>> -}
>>> -
>>> static irqreturn_t ucsi_stm32g0_irq_handler(int irq, void *data)
>>> {
>>> struct ucsi_stm32g0 *g0 = data;
>>> @@ -449,13 +416,7 @@ static irqreturn_t ucsi_stm32g0_irq_handler(int irq, void *data)
>>> if (ret)
>>> return IRQ_NONE;
>>>
>>> - if (UCSI_CCI_CONNECTOR(cci))
>>> - ucsi_connector_change(g0->ucsi, UCSI_CCI_CONNECTOR(cci));
>>> -
>>> - if (cci & UCSI_CCI_ACK_COMPLETE && test_and_clear_bit(ACK_PENDING, &g0->flags))
>>> - complete(&g0->complete);
>>> - if (cci & UCSI_CCI_COMMAND_COMPLETE && test_and_clear_bit(COMMAND_PENDING, &g0->flags))
>>> - complete(&g0->complete);
>>> + ucsi_notify_common(g0->ucsi, cci);
>>
>> I can see the fix "test_and_clear_bit()" sent earlier is removed from here.
>>
>> I'd suggest to use similar approach as here, unless you see some drawback?
>>
>> Please advise,
>> Best Regards,
>> Fabrice
>
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