linux-kernel - Re: [RESEND, PATCH 3/5] soc: mediatek: mtk-cmdq: Add cmdq_pkt_poll

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Date: Tue, 5 Mar 2024 03:51:21 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
	"matthias.bgg@...il.com" <matthias.bgg@...il.com>,
	Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	Singo Chang (張興國) <Singo.Chang@...iatek.com>,
	Jason-ch Chen (陳建豪)
	<Jason-ch.Chen@...iatek.com>, Shawn Sung (宋孝謙)
	<Shawn.Sung@...iatek.com>, Nancy Lin (林欣螢)
	<Nancy.Lin@...iatek.com>, Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>,
	"angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>
Subject: Re: [RESEND, PATCH 3/5] soc: mediatek: mtk-cmdq: Add
 cmdq_pkt_poll_addr() function

Hi, Jason:

On Tue, 2024-03-05 at 03:37 +0000, Jason-JH Lin (林睿祥) wrote:
> 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@...iatek.com>
> > > > > ---
> > > > >  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...

If ISP poll time longer than vblank, it may make display disorder. When
I see display disorder, could I find out ISP poll trigger this
disorder?

Regards,
CK

> 
> Regards,
> Jason-JH.Lin
> 
> > Regards,
> > CK
> >