linux-kernel - Re: [PATCH v5 4/7] mailbox: add MediaTek GPUEB IPI mailbox

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Message-ID: <CAPaKu7Tz9tw=fbz17kpPn1Pj_YsGRJZR9o28zkfiBgvxL3rdxg@mail.gmail.com>
Date: Fri, 3 Oct 2025 11:15:51 -0700
From: Chia-I Wu <olvaffe@...il.com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Boris Brezillon <boris.brezillon@...labora.com>, Jassi Brar <jassisinghbrar@...il.com>, 
	Chen-Yu Tsai <wenst@...omium.org>, Steven Price <steven.price@....com>, 
	Liviu Dudau <liviu.dudau@....com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>, kernel@...labora.com, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mediatek@...ts.infradead.org, linux-hardening@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v5 4/7] mailbox: add MediaTek GPUEB IPI mailbox

On Mon, Sep 29, 2025 at 12:47 AM Nicolas Frattaroli
<nicolas.frattaroli@...labora.com> wrote:
>
> The MT8196 SoC uses an embedded MCU to control frequencies and power of
> the GPU. This controller is referred to as "GPUEB".
>
> It communicates to the application processor, among other ways, through
> a mailbox.
>
> The mailbox exposes one interrupt, which appears to only be fired when a
> response is received, rather than a transaction is completed. For us,
> this means we unfortunately need to poll for txdone.
>
> The mailbox also requires the EB clock to be on when touching any of the
> mailbox registers.
>
> Add a simple driver for it based on the common mailbox framework.
>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Reviewed-by: Chia-I Wu <olvaffe@...il.com>
> ---
>  drivers/mailbox/Kconfig             |  10 ++
>  drivers/mailbox/Makefile            |   2 +
>  drivers/mailbox/mtk-gpueb-mailbox.c | 318 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 330 insertions(+)
[...]
> +static irqreturn_t mtk_gpueb_mbox_thread(int irq, void *data)
> +{
> +       struct mtk_gpueb_mbox_chan *ch = data;
> +       u8 buf[GPUEB_MBOX_MAX_RX_SIZE] = {};
nit: move to inside the if-block below.
> +       int status;
> +
> +       status = atomic_cmpxchg(&ch->rx_status, GPUEB_MBOX_FULL | GPUEB_MBOX_BLOCKED,
> +                               GPUEB_MBOX_FULL);
> +       if (status == (GPUEB_MBOX_FULL | GPUEB_MBOX_BLOCKED)) {
> +               mtk_gpueb_mbox_read_rx(buf, ch);
> +               writel(BIT(ch->num), ch->ebm->mbox_ctl + GPUEB_MBOX_CTL_IRQ_CLR);
> +               mbox_chan_received_data(&ch->ebm->mbox.chans[ch->num], buf);
> +               atomic_set(&ch->rx_status, 0);
> +               return IRQ_HANDLED;
> +       }
> +
> +       return IRQ_NONE;
> +}