linux-kernel - Re: [PATCH 1/3] dt-bindings: dma: mediatek,uart-dma: drop mediatek,dma-33bits property

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Message-ID: <OqrpnP1RyPRyuNfMPA0kXp64iZ1Q5a0ZDMKXz4xmzcg9U7s9SvEvuo1jmiNAwTCgCibt0r1EafrFMwj-ML0ByUC1nsh5ZVbsY1pfOF7pzq8=@proton.me>
Date: Tue, 23 Sep 2025 12:17:45 +0000
From: Max Shevchenko <wctrl@...ton.me>
To: Rob Herring <robh@...nel.org>
Cc: "sean.wang@...iatek.com" <sean.wang@...iatek.com>, "vkoul@...nel.org" <vkoul@...nel.org>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>, "matthias.bgg@...il.com" <matthias.bgg@...il.com>, "angelogioacchino.delregno@...labora.com" <angelogioacchino.delregno@...labora.com>, "long.cheng@...iatek.com" <long.cheng@...iatek.com>, "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] dt-bindings: dma: mediatek,uart-dma: drop mediatek,dma-33bits property

On Monday, September 22nd, 2025 at 11:47 PM, Rob Herring <robh@...nel.org> wrote:

> On Sun, Sep 21, 2025 at 02:03:40PM +0300, Max Shevchenko wrote:
> 
> > Many newer SoCs support more than 33 bits for DMA.
> > Drop the property in order to switch to the platform data.
> > 
> > The reference SoCs were taken from the downstream kernel (6.6) for
> > the MT6991 SoC.
> > 
> > Signed-off-by: Max Shevchenko wctrl@...ton.me
> > ---
> > Documentation/devicetree/bindings/dma/mediatek,uart-dma.yaml | 11 ++++-------
> > 1 file changed, 4 insertions(+), 7 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/dma/mediatek,uart-dma.yaml b/Documentation/devicetree/bindings/dma/mediatek,uart-dma.yaml
> > index dab468a88942d694525aa391f695c44d192f0c42..9dfdfe81af7edbe3540e4b757547a5d5e6ae810c 100644
> > --- a/Documentation/devicetree/bindings/dma/mediatek,uart-dma.yaml
> > +++ b/Documentation/devicetree/bindings/dma/mediatek,uart-dma.yaml
> > @@ -22,12 +22,14 @@ properties:
> > - items:
> > - enum:
> > - mediatek,mt2712-uart-dma
> > - - mediatek,mt6795-uart-dma
> > - mediatek,mt8365-uart-dma
> > - mediatek,mt8516-uart-dma
> > - const: mediatek,mt6577-uart-dma
> > - enum:
> > - - mediatek,mt6577-uart-dma
> > + - mediatek,mt6577-uart-dma # 32 bits
> > + - mediatek,mt6795-uart-dma # 33 bits
> 
> 
> Unless all existing s/w supported mediatek,mt6795-uart-dma, you just
> broke this platform which was relying on the fallback compatible.
> 


As of v6.17-rc6 and linux-next 20250922, the only user of the
mediatek,mt6795-uart-dma compatible is the MT6795 itself, which also
uses the mediatek,dma-33bits property. The second patch makes driver
to set the DMA bitmask based on the compatible.
Therefore I don't think it breaks the platform.

> > + - mediatek,mt6779-uart-dma # 34 bits
> > + - mediatek,mt6985-uart-dma # 35 bits
> > 
> > reg:
> > minItems: 1
> > @@ -56,10 +58,6 @@ properties:
> > Number of virtual channels of the UART APDMA controller
> > maximum: 16
> > 
> > - mediatek,dma-33bits:
> > - type: boolean
> > - description: Enable 33-bits UART APDMA support
> 
> 
> If this is in use, you need to mark it 'deprecated' instead.
> 


The same question here, third patch removes this property from its
sole user. Does it actually need to be marked as deprecated and
not deleted?

> > -
> > required:
> > - compatible
> > - reg
> > @@ -116,7 +114,6 @@ examples:
> > dma-requests = <12>;
> > clocks = <&pericfg CLK_PERI_AP_DMA>;
> > clock-names = "apdma";
> > - mediatek,dma-33bits;
> > #dma-cells = <1>;
> > };
> > };
> > 
> > --
> > 2.51.0

Sincerely,
Max