Date:   Tue, 31 Jan 2023 06:29:59 +0000
From:   Haotien Hsu <haotienh@...dia.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sing-Han Chen <singhanc@...dia.com>,
        Sanket Goswami <Sanket.Goswami@....com>,
        Wayne Chang <waynec@...dia.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] ucsi_ccg: Refine the UCSI Interrupt handling

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@...dia.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@...dia.com>
>> Signed-off-by: Haotien Hsu <haotienh@...dia.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
> 

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