Re: [RESEND, PATCH 3/5] soc: mediatek: mtk-cmdq: Add cmdq_pkt_poll_addr() function

[Jason-JH Lin (林睿祥)]

On Tue, 2024-03-05 at 03:26 +0000, CK Hu (胡俊光) wrote:
> Hi, Jason:
> 
> On Mon, 2024-03-04 at 16:04 +0000, Jason-JH Lin (林睿祥) wrote:
> > Hi CK,
> > 
> > Thanks for the reviews.
> > 
> > On Mon, 2024-03-04 at 03:11 +0000, CK Hu (胡俊光) wrote:
> > > Hi, Jason:
> > > 
> > > On Fri, 2024-03-01 at 22:44 +0800, Jason-JH.Lin wrote:
> > > > Add cmdq_pkt_poll_addr function to support CMDQ user making
> > > > an instruction for polling a specific address of hardware
> > > > rigster
> > > > to check the value with or without mask.
> > > > 
> > > > POLL is an old operation in GCE, so it does not support SPR and
> > > > CMDQ_CODE_LOGIC. CMDQ users need to use GPR and CMDQ_CODE_MASK
> > > > to move polling register address to GPR to make an instruction.
> > > > This will be done in cmdq_pkt_poll_addr().
> > > > 
> > > > Signed-off-by: Jason-JH.Lin <jason-jh.lin@xxxxxxxxxxxx>
> > > > ---
> > > >  drivers/soc/mediatek/mtk-cmdq-helper.c | 38
> > > > ++++++++++++++++++++++++++
> > > >  include/linux/soc/mediatek/mtk-cmdq.h  | 16 +++++++++++
> > > >  2 files changed, 54 insertions(+)
> > > > 
> > > > diff --git a/drivers/soc/mediatek/mtk-cmdq-helper.c
> > > > b/drivers/soc/mediatek/mtk-cmdq-helper.c
> > > > index 3a1e47ad8a41..2e9fc9bb1183 100644
> > > > --- a/drivers/soc/mediatek/mtk-cmdq-helper.c
> > > > +++ b/drivers/soc/mediatek/mtk-cmdq-helper.c
> > > > @@ -12,6 +12,7 @@
> > > >  
> > > >  #define CMDQ_WRITE_ENABLE_MASK	BIT(0)
> > > >  #define CMDQ_POLL_ENABLE_MASK	BIT(0)
> > > > +#define CMDQ_POLL_HIGH_ADDR_GPR	(14)
> > > 
> > > I think there are multiple GPR and you use #14 to store high
> > > addr.
> > > I
> > > would like you to list all GPR and do not limit the usage of each
> > > GPR.
> > > The question is, why limit #14 to be high addr? If the GPR is
> > > shared
> > > by
> > > all threads, there should be a mechanism to manage GPR usage for
> > > client
> > > driver to allocate/free GPR.
> > 
> > Yes, there are 16 GPR, from GPR_R0 ~ GPR_R15 and they are shared by
> > all
> > threads, but GPR_R0 and GPR_R1 is used by GCE HW itself.
> > 
> > I think user may not know which GPR is available, so I think CMDQ
> > driver should manage the usage of GPR instead of configure by the
> > user.
> > 
> > Currently, we only use 1 dedicated GPR in poll, so I defined it in
> > CMDQ
> > driver to make it simpler.
> 
> If thread 1 poll addr A first, GPR is set to A. But poll time exceed
> GCE_THD_SLOT_CYCLES, change to thread 2 and thread 2 poll addr B, GPR
> is set to B. Later switch to thread A and GCE would execute poll
> command and GPR is B, so thread 1 would poll addr B, but this is
> wrong.
> How do you solve this problem?
> 
If POLL instruction has timeout, this may be a problem.

But POLL is a legacy operation, it won't context switch when the
execute time exceed GCE_THR_SLOT_CYCLES. So we add the comment "All GCE
hardware threads will be blocked by this instruction" in the kerneldoc.

And currently, we don't set the GCE hardware timeout in
CMDQ_THR_INST_TIMEOUT_CYCLES, so it'll poll forever until the polling
value is set...

Regards,
Jason-JH.Lin

> Regards,
> CK
>