Re: [PATCH v4] ucsi_ccg: Refine the UCSI Interrupt handling

Haotien Hsu
2023-01-31T06:30:06Z

On 1/19/23 20:28, Greg Kroah-Hartman wrote:
> External email: Use caution opening links or attachments
>
>
> On Wed, Jan 18, 2023 at 02:15:23PM +0800, Haotien Hsu wrote:
>> From: Sing-Han Chen <singhanc@nvidia.com>
>>
>> For the CCGx, when the OPM field in the INTR_REG is cleared, then the
>> CCI data in the PPM is reset.
>>
>> To align with the CCGx UCSI interface guide, this patch updates the
>> driver to copy CCI and MESSAGE_IN before clearing UCSI interrupt.
>> When a new command is sent, the driver will clear the old CCI and
>> MESSAGE_IN copy.
>>
>> Finally, clear UCSI_READ_INT before calling complete() to ensure that
>> the ucsi_ccg_sync_write() would wait for the interrupt handling to
>> complete.
>> It prevents the driver from resetting CCI prematurely.
>>
>> Signed-off-by: Sing-Han Chen <singhanc@nvidia.com>
>> Signed-off-by: Haotien Hsu <haotienh@nvidia.com>
>> ---
>> V1->V2
>> - Fix uninitialized symbol 'cci'
>> v2->v3
>> - Remove misusing Reported-by tags
>> v3->v4
>> - Add comments for op_lock
>> ---
>> drivers/usb/typec/ucsi/ucsi_ccg.c | 90 ++++++++++++++++++++++++++++---
>> 1 file changed, 83 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/usb/typec/ucsi/ucsi_ccg.c b/drivers/usb/typec/ucsi/ucsi_ccg.c
>> index eab3012e1b01..532813a32cc1 100644
>> --- a/drivers/usb/typec/ucsi/ucsi_ccg.c
>> +++ b/drivers/usb/typec/ucsi/ucsi_ccg.c
>> @@ -192,6 +192,12 @@ struct ucsi_ccg_altmode {
>> bool checked;
>> } __packed;
>>
>> +#define CCGX_MESSAGE_IN_MAX 4
>> +struct op_region {
>> + u32 cci;
>
> This is coming from hardware so you have to specify the endian-ness of
> it, right?

Yes.
According to CCGX's guide, CCI and MESSAGE_IN are accessed as registers.

>
>> + u32 message_in[CCGX_MESSAGE_IN_MAX];
>
> Same here.
>
>> +};
>> +
>> struct ucsi_ccg {
>> struct device *dev;
>> struct ucsi *ucsi;
>> @@ -222,6 +228,13 @@ struct ucsi_ccg {
>> bool has_multiple_dp;
>> struct ucsi_ccg_altmode orig[UCSI_MAX_ALTMODES];
>> struct ucsi_ccg_altmode updated[UCSI_MAX_ALTMODES];
>> +
>> + /*
>> + * This spinlock protects op_data which includes CCI and MESSAGE_IN that
>> + * will be updated in ISR
>> + */
>> + spinlock_t op_lock;
>> + struct op_region op_data;
>> };
>>
>> static int ccg_read(struct ucsi_ccg *uc, u16 rab, u8 *data, u32 len)
>> @@ -305,12 +318,57 @@ static int ccg_write(struct ucsi_ccg *uc, u16 rab, const u8 *data, u32 len)
>> return 0;
>> }
>>
>> +static void ccg_op_region_read(struct ucsi_ccg *uc, unsigned int offset,
>> + void *val, size_t val_len)
>> +{
>> + struct op_region *data = &uc->op_data;
>> +
>> + spin_lock(&uc->op_lock);
>> + if (offset == UCSI_CCI)
>> + memcpy(val, &data->cci, val_len);
>> + else if (offset == UCSI_MESSAGE_IN)
>> + memcpy(val, &data->message_in, val_len);
>
> What happens if the offset is neither of these?
>
> You seem to be only calling this if that value is set correctly, but
> this seems very fragile. You are also only calling this in one place,
> so why is this a function at all? Just do the copy under the lock as
> needed in the calling location instead.
>

I will move these codes inline.

>> + spin_unlock(&uc->op_lock);
>> +}
>> +
>> +static void ccg_op_region_update(struct ucsi_ccg *uc, u32 cci)
>> +{
>> + u16 reg = CCGX_RAB_UCSI_DATA_BLOCK(UCSI_MESSAGE_IN);
>> + struct op_region *data = &uc->op_data;
>> + u32 message_in[CCGX_MESSAGE_IN_MAX];
>
> Are you sure you can put this big of a buffer on the stack?
>

I assume 16 bytes are okay to put on the stack.
Please let me know if you think this size is not practical to put on the
stack.

>> +
>> + if (UCSI_CCI_LENGTH(cci))
>> + if (ccg_read(uc, reg, (void *)&message_in,
>> + sizeof(message_in))) {
>
> Are you allowed to copy in into stack memory? This ends up being an i2c
> message, right? Can that be transferred into non-dma-able memory?
>

Yes, it works.

>> + dev_err(uc->dev, "failed to read MESSAGE_IN\n");
>
> Why can you not fail this function? You are throwing away the error
> here, that's not good.
>

I will update it to return errors.

>> + return;
>> + }
>> +
>> + spin_lock(&uc->op_lock);
>> + memcpy(&data->cci, &cci, sizeof(cci));
>
> Perhaps just:
> data->cci = cci;
> as this is only a 32bit value.
>

True.
>> + if (UCSI_CCI_LENGTH(cci))
>> + memcpy(&data->message_in, &message_in, sizeof(message_in));
>> + spin_unlock(&uc->op_lock);
>> +}
>> +
>> +static void ccg_op_region_clean(struct ucsi_ccg *uc)
>> +{
>> + struct op_region *data = &uc->op_data;
>> +
>> + spin_lock(&uc->op_lock);
>> + memset(&data->cci, 0, sizeof(data->cci));
>
> data->cci = 0;
>
>> + memset(&data->message_in, 0, sizeof(data->message_in));
>
> Or better yet, do it all at once:
> memset(&data, 0, sizeof(*data));

That looks better, thanks.

>
>> + spin_unlock(&uc->op_lock);
>
> But why do you need to do this at all? Why "clean" the whole buffer
> out, why not just set cci to 0 and be done with it?
>
> Or why even clean this out at all, what happens if you do not?
>

It only be called in ucsi_ccg_async_write(), and I will move it there as
inline.
The reason to clean the whole op_data is that UCSI may read MESSAGE_IN
after writing UCSI_CONTROL, so clear it to avoid callers getting wrong data.

>> +}
>> +
>> static int ucsi_ccg_init(struct ucsi_ccg *uc)
>> {
>> unsigned int count = 10;
>> u8 data;
>> int status;
>>
>> + spin_lock_init(&uc->op_lock);
>> +
>> data = CCGX_RAB_UCSI_CONTROL_STOP;
>> status = ccg_write(uc, CCGX_RAB_UCSI_CONTROL, &data, sizeof(data));
>> if (status < 0)
>> @@ -520,9 +578,13 @@ static int ucsi_ccg_read(struct ucsi *ucsi, unsigned int offset,
>> u16 reg = CCGX_RAB_UCSI_DATA_BLOCK(offset);
>> struct ucsi_capability *cap;
>> struct ucsi_altmode *alt;
>> - int ret;
>> + int ret = 0;
>> +
>> + if ((offset == UCSI_CCI) || (offset == UCSI_MESSAGE_IN))
>> + ccg_op_region_read(uc, offset, val, val_len);
>> + else
>> + ret = ccg_read(uc, reg, val, val_len);
>>
>> - ret = ccg_read(uc, reg, val, val_len);
>> if (ret)
>> return ret;
>>
>> @@ -559,9 +621,13 @@ static int ucsi_ccg_read(struct ucsi *ucsi, unsigned int offset,
>> static int ucsi_ccg_async_write(struct ucsi *ucsi, unsigned int offset,
>> const void *val, size_t val_len)
>> {
>> + struct ucsi_ccg *uc = ucsi_get_drvdata(ucsi);
>> u16 reg = CCGX_RAB_UCSI_DATA_BLOCK(offset);
>>
>> - return ccg_write(ucsi_get_drvdata(ucsi), reg, val, val_len);
>> + if (offset == UCSI_CONTROL)
>> + ccg_op_region_clean(uc);
>
> Why is this needed? You have not documented it the need for this.
>

The reason is described as above and I will add comments for it.

> thanks,
>
> greg k-h
>