linux-kernel - Re: [PATCH v4 6/8] soc: mediatek: Add programming flow for unsupported subsys ID hardware

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Message-ID: <451d1b8a5aed46fd119c546f15fe00371f9546f3.camel@mediatek.com>
Date: Thu, 6 Mar 2025 11:05:22 +0000
From: Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>
To: "robh@...nel.org" <robh@...nel.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, AngeloGioacchino Del Regno
	<angelogioacchino.delregno@...labora.com>, "conor+dt@...nel.org"
	<conor+dt@...nel.org>, "mchehab@...nel.org" <mchehab@...nel.org>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
	"jassisinghbrar@...il.com" <jassisinghbrar@...il.com>
CC: "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	Sirius Wang (王皓昱) <Sirius.Wang@...iatek.com>,
	Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
	Xiandong Wang (王先冬)
	<Xiandong.Wang@...iatek.com>, "linux-mediatek@...ts.infradead.org"
	<linux-mediatek@...ts.infradead.org>, Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Moudy Ho (何宗原) <Moudy.Ho@...iatek.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"fshao@...omium.org" <fshao@...omium.org>,
	Singo Chang (張興國) <Singo.Chang@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>,
	Xavier Chang (張獻文) <Xavier.Chang@...iatek.com>,
	"matthias.bgg@...il.com" <matthias.bgg@...il.com>, "treapking@...omium.org"
	<treapking@...omium.org>
Subject: Re: [PATCH v4 6/8] soc: mediatek: Add programming flow for
 unsupported subsys ID hardware

On Wed, 2025-03-05 at 19:08 +0100, AngeloGioacchino Del Regno wrote:
> 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
> 
> 
> Il 05/03/25 17:12, Jason-JH Lin (林睿祥) ha scritto:
> > On Tue, 2025-03-04 at 10:41 +0100, AngeloGioacchino Del Regno
> > wrote:
> > > 
> > > External email : Please do not click links or open attachments
> > > until
> > > you have verified the sender or the content.
> > > 
> > > 
> > > Il 18/02/25 06:41, Jason-JH Lin ha scritto:
> > > > To support hardware without subsys IDs on new SoCs, add a
> > > > programming
> > > > flow that checks whether the subsys ID is valid. If the subsys
> > > > ID
> > > > is
> > > > invalid, the flow will call 2 alternative CMDQ APIs:
> > > > cmdq_pkt_assign() and cmdq_pkt_write_s_value() to achieve the
> > > > same
> > > > functionality.
> > > > 
> > > > Signed-off-by: Jason-JH Lin <jason-jh.lin@...iatek.com>
> > > > ---
> > > >    drivers/soc/mediatek/mtk-mmsys.c | 14 +++++++++++---
> > > >    drivers/soc/mediatek/mtk-mutex.c | 11 +++++++++--
> > > >    2 files changed, 20 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/drivers/soc/mediatek/mtk-mmsys.c
> > > > b/drivers/soc/mediatek/mtk-mmsys.c
> > > > index bb4639ca0b8c..ce949b863b05 100644
> > > > --- a/drivers/soc/mediatek/mtk-mmsys.c
> > > > +++ b/drivers/soc/mediatek/mtk-mmsys.c
> > > > @@ -167,9 +167,17 @@ static void mtk_mmsys_update_bits(struct
> > > > mtk_mmsys *mmsys, u32 offset, u32 mask,
> > > >        u32 tmp;
> > > > 
> > > >        if (mmsys->cmdq_base.size && cmdq_pkt) {
> > > > -             ret = cmdq_pkt_write_mask(cmdq_pkt, mmsys-
> > > > > cmdq_base.subsys,
> > > > -                                       mmsys->cmdq_base.offset
> > > > +
> > > > offset, val,
> > > > -                                       mask);
> > > > +             offset += mmsys->cmdq_base.offset;
> > > > +             if (mmsys->cmdq_base.subsys !=
> > > > CMDQ_SUBSYS_INVALID) {
> > > 
> > > You're still anyway passing the subsys to cmdq_pkt_write_mask(),
> > > right?!
> > > Why don't you just handle this in cmdq_pkt_write_mask() then? ;-)
> > > 
> > > I can see this pattern being repeated over and over in both
> > > drm/mediatek and MDP3
> > > drivers, and it's not necessary to duplicate this many times when
> > > you
> > > can write it
> > > just once.
> > > 
> > > Would've also been faster for you to implement... :-D
> > > 
> > 
> > I think did it in the series V1:
> > https://patchwork.kernel.org/project/linux-mediatek/patch/20241121042602.32730-5-jason-jh.lin@mediatek.com
> > 
> > Because it'll need to passing the base_pa and that will need to
> > change
> > the interface for original APIs.
> > 
> > And CK think that's not a necessary to change the APIs. It can be
> > done
> > by cmdq_pkt_assign() + cmdq_pkt_write_s_mask_value() in the client
> > drivers. Then you can see this pattern in everywhere. :-)
> > 
> 
> Using likely(x) and unlikely(x) should be avoided, really, unless
> it's something
> that is really really really really ... really ... rea.... likely or
> unlikely :-)
> 
> Btw. Changing the APIs is a bit difficult, but I disagree with CK
> about not
> "inventing" a new API for the unsupported-subsys flow.
> 
> It's true, it is not *strictly* needed to add a function, but it's
> good for any
> kind of future maintainability - as I explained, it's easier then to
> fix a problem
> if there's one.... and well, I can see that you agree with me,
> because effectively
> you did it the first time :-)
> 
> CK mentioned using cmdq_pkt_write() *or*
> cmdq_pkt_assignwrite/cmdq_pkt_write_pa()
> (however you wanna call it, it's fine for me), in drivers that know
> that there
> always is or there always isn't a subsys ID: that's a good
> suggestion, as this can
> be eventually done with assigning a function pointer, so, no
> conditionals at each
> operation.
> 
> My point of view, finally, is:
>   - This is just another way of doing cmdq_pkt_write()
>     - This, at the end of the day, does exactly what cmdq_pkt_write()
> is doing,
>       except it's doing it with two instructions instead of one;
>   - The same thing can be done in two different ways (depending on
> SoC)
>     - This same thing should have a function that does it.
> 
> A function that does it can be
> 
> int cmdq_pkt_write_pa(struct cmdq_pkt *pkt, u8 subsys /*unused*/, u32
> pa_base, u16
> offset, u32 value)
> {
>         err = cmdq_pkt_assign(pkt, 0, CMDQ_ADDR_HIGH(pa_base));
>         if (err < 0)
>                 return err;
> 
>         return cmdq_pkt_write_s_value( .... etc)
> }
> 
> int cmdq_pkt_write() <--- unchanged, scheduled for removal after all
> drivers migrated
> 
> int cmdq_pkt_write_subsys(struct cmdq_pkt *pkt, u8 subsys, u32
> pa_base /*unused*/,
> u16 offset, u32 value)
> {
>         /* This function will get the contents of cmdq_pkt_write once
> removed,
>             but, in the meanwhile, to avoid duplication we just call
> that: */
> 
>         return cmdq_pkt_write(pkt, subsys, offset, value);
> }
> 
> - Are we adding one more function parameter? Yes
> - Is this impacting performance overall? Not really
> 
> After all, we're living in an ARMv8 (actually, ARMv9 for new ones)
> world, so
> one more function param won't hurt anyone.
> 
> I think that's the best of both worlds, and makes everyone happy.
> Are you happy with that? :-)
> 

Yes, I am happy with that. :-)
And thanks for your detail coding.

I'll change it in the next version.

regards,
Jason-JH Lin

> Cheers,
> Angelo
>