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

Greg Kroah-Hartman
2023-01-31T06:47:14Z

On Tue, Jan 31, 2023 at 06:29:59AM +0000, Haotien Hsu wrote:
> 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.

So please specify the endianness of the registers.

> >> +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.

Why do you want it on the stack? Is it going to be used as DMA memory?
If so, it can NOT be 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.

How was this tested? On a system that requires i2c messages to be in
DMA?

> >> + 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.

How could a caller get the wrong data? It's what they asked for. I'm
confused.

greg k-h