linux-kernel - Re: [RESEND, PATCH 4/5] soc: mediatek: mtk-cmdq: Add cmdq_pkt_acquire

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Date: Mon, 4 Mar 2024 15:39:20 +0000
From: Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>,
	"jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
	"matthias.bgg@...il.com" <matthias.bgg@...il.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 4/5] soc: mediatek: mtk-cmdq: Add
 cmdq_pkt_acquire_event() function

Hi CK,

Thanks for the reviews.

On Mon, 2024-03-04 at 02:11 +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_acquire_event() function to support CMDQ user making
> > an instruction for acquiring event.
> > 
> > CMDQ users can use cmdq_pkt_acquire_event() and
> > cmdq_pkt_clear_event()
> > to acquire GCE event and release GCE event and achieve the
> > MUTEX_LOCK
> > protection between GCE threads.
> 
> I'm not clear what acquire do in detail. This is what I guess:
> 
> cmdq_pkt_acquire_event() would wait for event to be cleared. After
> event is cleared, cmdq_pkt_acquire_event() would set event and keep
> executing next command. So the mutex would work like this
> 
> cmdq_pkt_acquire_event() /* mutex lock */
> 
> /* critical secton */
> 
> cmdq_pkt_clear_event() /* mutex unlock */
> 
> If it's so, describe as detail as this. If not, describe how it do.
> 
Yes, they should be used like this.
I'll add more description in commit message.

> As I know, GCE is single core, so multiple thread is served by single
> GCE, why need mutex lock?
> 
Although GCE is single core, it will context switch to other GCE
threads with the same priority. The context switch time is set to
GCE_THR_SLOT_CYCLES during GCE initialization.

So we have to use event_lock to protect HW resource if each cmdq_pkt in
different thread may execute more than the context switch time.

Regards,
Jason-JH.Lin

> Regards,
> CK
> 
> > 
> > Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> > ---
> >  drivers/soc/mediatek/mtk-cmdq-helper.c | 15 +++++++++++++++
> >  include/linux/soc/mediatek/mtk-cmdq.h  |  9 +++++++++
> >  2 files changed, 24 insertions(+)
> > 
> > diff --git a/drivers/soc/mediatek/mtk-cmdq-helper.c
> > b/drivers/soc/mediatek/mtk-cmdq-helper.c
> > index 2e9fc9bb1183..0183b40a0eff 100644
> > --- a/drivers/soc/mediatek/mtk-cmdq-helper.c
> > +++ b/drivers/soc/mediatek/mtk-cmdq-helper.c
> > @@ -342,6 +342,21 @@ int cmdq_pkt_wfe(struct cmdq_pkt *pkt, u16
> > event, bool clear)
> >  }
> >  EXPORT_SYMBOL(cmdq_pkt_wfe);
> >  
> > +int cmdq_pkt_acquire_event(struct cmdq_pkt *pkt, u16 event)
> > +{
> > +	struct cmdq_instruction inst = {};
> > +
> > +	if (event >= CMDQ_MAX_EVENT)
> > +		return -EINVAL;
> > +
> > +	inst.op = CMDQ_CODE_WFE;
> > +	inst.value = CMDQ_WFE_UPDATE | CMDQ_WFE_UPDATE_VALUE |
> > CMDQ_WFE_WAIT;
> > +	inst.event = event;
> > +
> > +	return cmdq_pkt_append_command(pkt, inst);
> > +}
> > +EXPORT_SYMBOL(cmdq_pkt_acquire_event);
> > +
> >  int cmdq_pkt_clear_event(struct cmdq_pkt *pkt, u16 event)
> >  {
> >  	struct cmdq_instruction inst = { {0} };
> > diff --git a/include/linux/soc/mediatek/mtk-cmdq.h
> > b/include/linux/soc/mediatek/mtk-cmdq.h
> > index 2fe9be240fbc..de93c0a8e8a9 100644
> > --- a/include/linux/soc/mediatek/mtk-cmdq.h
> > +++ b/include/linux/soc/mediatek/mtk-cmdq.h
> > @@ -202,6 +202,15 @@ int cmdq_pkt_mem_move(struct cmdq_pkt *pkt,
> > dma_addr_t src_addr, dma_addr_t dst_
> >   */
> >  int cmdq_pkt_wfe(struct cmdq_pkt *pkt, u16 event, bool clear);
> >  
> > +/**
> > + * cmdq_pkt_acquire_event() - append acquire event command to the
> > CMDQ packet
> > + * @pkt:	the CMDQ packet
> > + * @event:	the desired event to be acquired
> > + *
> > + * Return: 0 for success; else the error code is returned
> > + */
> > +int cmdq_pkt_acquire_event(struct cmdq_pkt *pkt, u16 event);
> > +
> >  /**
> >   * cmdq_pkt_clear_event() - append clear event command to the CMDQ
> > packet
> >   * @pkt:	the CMDQ packet