linux-kernel - Re: [PATCH v7 02/20] mailbox: mtk-cmdq: Refine DMA address handling for the command buffer

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Message-ID: <9f87c7826731329e3a67cbf3104d02ead83825dd.camel@mediatek.com>
Date: Mon, 13 Oct 2025 06:09:39 +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>, "nicolas@...fresne.ca" <nicolas@...fresne.ca>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Paul-pl Chen (陳柏霖) <Paul-pl.Chen@...iatek.com>,
	Moudy Ho (何宗原) <Moudy.Ho@...iatek.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Singo Chang (張興國) <Singo.Chang@...iatek.com>,
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	<linux-arm-kernel@...ts.infradead.org>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>
Subject: Re: [PATCH v7 02/20] mailbox: mtk-cmdq: Refine DMA address handling
 for the command buffer

On Thu, 2025-10-09 at 13:27 +0200, AngeloGioacchino Del Regno wrote:
> 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
> 
> 
> Il 27/08/25 13:37, Jason-JH Lin ha scritto:
> > GCE can only fetch the command buffer address from a 32-bit
> > register.
> > Some SoCs support a 35-bit command buffer address for GCE, which
> > requires a right shift of 3 bits before setting the address into
> > the 32-bit register. A comment has been added to the header of
> > cmdq_get_shift_pa() to explain this requirement.
> > 
> > To prevent the GCE command buffer address from being DMA mapped
> > beyond
> > its supported bit range, the DMA bit mask for the device is set
> > during
> > initialization.
> > 
> > Additionally, to ensure the correct shift is applied when setting
> > or
> > reading the register that stores the GCE command buffer address,
> > new APIs, cmdq_reg_shift_addr() and cmdq_reg_revert_addr(), have
> > been
> > introduced for consistent operations on this register.
> > 
> > The variable type for the command buffer address has been
> > standardized
> > to dma_addr_t to prevent handling issues caused by type mismatches.
> > 
> > Fixes: 0858fde496f8 ("mailbox: cmdq: variablize address shift in
> > platform")
> > Signed-off-by: Jason-JH Lin <jason-jh.lin@...iatek.com>
> > ---
> >   drivers/mailbox/mtk-cmdq-mailbox.c       | 43 ++++++++++++++++---
> > -----
> >   include/linux/mailbox/mtk-cmdq-mailbox.h | 10 ++++++
> >   2 files changed, 39 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/mailbox/mtk-cmdq-mailbox.c
> > b/drivers/mailbox/mtk-cmdq-mailbox.c
> > index 532929916e99..a60486cbb533 100644
> > --- a/drivers/mailbox/mtk-cmdq-mailbox.c
> > +++ b/drivers/mailbox/mtk-cmdq-mailbox.c
> > @@ -92,6 +92,16 @@ struct gce_plat {
> >       u32 gce_num;
> >   };
> > 
> > +static inline u32 cmdq_reg_shift_addr(dma_addr_t addr, const
> > struct gce_plat *pdata)
> 
> cmdq_format_gce_addr() or cmdq_pa_to_gce_addr()
> 
> (or cmdq_va_to_gce_addr() if this is not a physical address)
> 
> explains what you're doing here a bit better I think.

OK, I'll change the API name and add comments for both APIs:

static inline u32 cmdq_convert_gce_addr()
{
    /* Convert DMA addr (PA or IOVA) to GCE readable addr */
}

static inline u32 cmdq_revert_gce_addr()
{
    /* Revert GCE readable addr to DMA addr (PA or IOVA) */
}

> 
> > +{
> > +     return (addr >> pdata->shift);
> 
> You don't need parenthesis; just `return addr >> pdata->shift;` is
> fine
> 

OK, I'll remove this.

> > +}
> > +
> > +static inline dma_addr_t cmdq_reg_revert_addr(u32 addr, const
> > struct gce_plat *pdata)
> 
> cmdq_gce_to_pa_addr() or cmdq_get_pa_addr() perhaps? :-)
> 
> (same comments for s/pa/va/g if this is not physical address)
> 
> Everything else looks ok.
> 

Thanks for the reviews!

Regards,
Jason-JH Lin

> Cheers,
> Angelo