Re: [PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines
On Mon, Jun 19, 2023 at 12:19:58PM +0200, Miquel Raynal wrote:
> Hi Maxime,
>
> max...@cerno.tech wrote on Mon, 19 Jun 2023 11:39:56 +0200:
>
> > On Sun, Jun 18, 2023 at 07:37:32PM +0200, Miquel Raynal wrote:
> > > Hello Maxime,
> > >
> > > max...@cerno.tech wrote on Sun, 18 Jun 2023 16:37:58 +0200:
> > >
> > > > Hi,
> > > >
> > > > On Fri, Jun 16, 2023 at 06:32:51PM +0200, Miquel Raynal wrote:
> > > > > The ST7789V LCD controller supports regular SPI wiring, as well as no
> > > > > Rx
> > > > > data line at all. The operating system needs to know whether it can
> > > > > read
> > > > > registers from the device or not. Let's detail this specific design
> > > > > possibility by bounding the spi-rx-bus-width property.
> > > > >
> > > > > Signed-off-by: Miquel Raynal
> > > > > ---
> > > > > .../devicetree/bindings/display/panel/sitronix,st7789v.yaml | 4
> > > > >
> > > > > 1 file changed, 4 insertions(+)
> > > > >
> > > > > diff --git
> > > > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > >
> > > > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > > index 0ccf0487fd8e..a25df7e1df88 100644
> > > > > ---
> > > > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > > +++
> > > > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > > @@ -29,6 +29,10 @@ properties:
> > > > >spi-cpha: true
> > > > >spi-cpol: true
> > > > >
> > > > > + spi-rx-bus-width:
> > > > > +minimum: 0
> > > > > +maximum: 1
> > > > > +
> > > >
> > > > It's not clear to me what the default would be?
> > >
> > > This binding references spi-peripheral-props.yaml which sets the
> > > default to 1, I believe it is sane to keep it that way?
> >
> > I'm not sure.
> >
> > The driver didn't need RX before, and we didn't have any property that
> > was expressing whether we had MISO in the device tree.
> >
> > That means we had both devices with and without MISO expressed in the
> > same way, the driver handling both (by ignoring MISO entirely).
> >
> > With this patch, you now introduce a property that specifies whether
> > MISO is connected or not, and defaults to MISO being there. And a later
> > patch will use MISO if it's available.
> >
> > This means that, while it's working fine for devices that had MISO
> > connected, devices that didn't are assumed to have it, and the driver
> > makes use of it.
>
> Ah yes, I get your concern. I thought you wanted to talk about the fact
> that it was not constrained in the yaml description. Your concern is
> about breaking existing devices.
>
> Your concern is real, designs not wiring the MISO line which do not
> describe this in the device tree will no longer succeed to probe with
> the current implementation. Technically speaking, they're broken since
> 2021:
>
> c476d430bfc0 ("dt-bindings: display: Add SPI peripheral schema to SPI based
> displays")
I mean, I guess, but an old DT was still booting fine. Validation didn't
pass but that's a bit irrelevant for devices that shipped already.
> We actually discussed this with Sebastian, right there:
> https://lore.kernel.org/all/20230609145951.853533-6-miquel.ray...@bootlin.com/T/#m9286cdb4d617c5efc29052b552e981ecfa2628e4
>
> And the conclusion was that we decided not to care about the broken
> descriptions (because, let's agree on this, not wiring the MISO line is
> not a standard spi design).
It might not be, but it's there. Just like the 9 bits per word :)
All the current in-tree users seem to only mux (at least, I haven't
checked the design) MOSI, and the devices I worked on with this driver
also didn't iirc.
> But I don't have a strong opinion TBH, so if you think it's best to
> prevent these probes from failing (note that I already added a debug
> line explicitly saying why the probe would fail, "easy" to identify)
> I'm fine turning the check as a warning and ignoring the error to
> avoid failing.
Updating the DT isn't always an option, so yeah, please make it backward
compatible.
Maxime
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Re: [PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines
Hi Maxime,
max...@cerno.tech wrote on Mon, 19 Jun 2023 11:39:56 +0200:
> On Sun, Jun 18, 2023 at 07:37:32PM +0200, Miquel Raynal wrote:
> > Hello Maxime,
> >
> > max...@cerno.tech wrote on Sun, 18 Jun 2023 16:37:58 +0200:
> >
> > > Hi,
> > >
> > > On Fri, Jun 16, 2023 at 06:32:51PM +0200, Miquel Raynal wrote:
> > > > The ST7789V LCD controller supports regular SPI wiring, as well as no Rx
> > > > data line at all. The operating system needs to know whether it can read
> > > > registers from the device or not. Let's detail this specific design
> > > > possibility by bounding the spi-rx-bus-width property.
> > > >
> > > > Signed-off-by: Miquel Raynal
> > > > ---
> > > > .../devicetree/bindings/display/panel/sitronix,st7789v.yaml | 4
> > > > 1 file changed, 4 insertions(+)
> > > >
> > > > diff --git
> > > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > index 0ccf0487fd8e..a25df7e1df88 100644
> > > > ---
> > > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > +++
> > > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml
> > > > @@ -29,6 +29,10 @@ properties:
> > > >spi-cpha: true
> > > >spi-cpol: true
> > > >
> > > > + spi-rx-bus-width:
> > > > +minimum: 0
> > > > +maximum: 1
> > > > +
> > >
> > > It's not clear to me what the default would be?
> >
> > This binding references spi-peripheral-props.yaml which sets the
> > default to 1, I believe it is sane to keep it that way?
>
> I'm not sure.
>
> The driver didn't need RX before, and we didn't have any property that
> was expressing whether we had MISO in the device tree.
>
> That means we had both devices with and without MISO expressed in the
> same way, the driver handling both (by ignoring MISO entirely).
>
> With this patch, you now introduce a property that specifies whether
> MISO is connected or not, and defaults to MISO being there. And a later
> patch will use MISO if it's available.
>
> This means that, while it's working fine for devices that had MISO
> connected, devices that didn't are assumed to have it, and the driver
> makes use of it.
Ah yes, I get your concern. I thought you wanted to talk about the fact
that it was not constrained in the yaml description. Your concern is
about breaking existing devices.
Your concern is real, designs not wiring the MISO line which do not
describe this in the device tree will no longer succeed to probe with
the current implementation. Technically speaking, they're broken since
2021:
c476d430bfc0 ("dt-bindings: display: Add SPI peripheral schema to SPI based
displays")
We actually discussed this with Sebastian, right there:
https://lore.kernel.org/all/20230609145951.853533-6-miquel.ray...@bootlin.com/T/#m9286cdb4d617c5efc29052b552e981ecfa2628e4
And the conclusion was that we decided not to care about the broken
descriptions (because, let's agree on this, not wiring the MISO line is
not a standard spi design). But I don't have a strong opinion TBH, so
if you think it's best to prevent these probes from failing (note that
I already added a debug line explicitly saying why the probe would
fail, "easy" to identify) I'm fine turning the check as a warning and
ignoring the error to avoid failing.
Thanks,
Miquèl
Re: [PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines
On Sun, Jun 18, 2023 at 07:37:32PM +0200, Miquel Raynal wrote: > Hello Maxime, > > max...@cerno.tech wrote on Sun, 18 Jun 2023 16:37:58 +0200: > > > Hi, > > > > On Fri, Jun 16, 2023 at 06:32:51PM +0200, Miquel Raynal wrote: > > > The ST7789V LCD controller supports regular SPI wiring, as well as no Rx > > > data line at all. The operating system needs to know whether it can read > > > registers from the device or not. Let's detail this specific design > > > possibility by bounding the spi-rx-bus-width property. > > > > > > Signed-off-by: Miquel Raynal > > > --- > > > .../devicetree/bindings/display/panel/sitronix,st7789v.yaml | 4 > > > 1 file changed, 4 insertions(+) > > > > > > diff --git > > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > > index 0ccf0487fd8e..a25df7e1df88 100644 > > > --- > > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > > +++ > > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > > @@ -29,6 +29,10 @@ properties: > > >spi-cpha: true > > >spi-cpol: true > > > > > > + spi-rx-bus-width: > > > +minimum: 0 > > > +maximum: 1 > > > + > > > > It's not clear to me what the default would be? > > This binding references spi-peripheral-props.yaml which sets the > default to 1, I believe it is sane to keep it that way? I'm not sure. The driver didn't need RX before, and we didn't have any property that was expressing whether we had MISO in the device tree. That means we had both devices with and without MISO expressed in the same way, the driver handling both (by ignoring MISO entirely). With this patch, you now introduce a property that specifies whether MISO is connected or not, and defaults to MISO being there. And a later patch will use MISO if it's available. This means that, while it's working fine for devices that had MISO connected, devices that didn't are assumed to have it, and the driver makes use of it. Maxime signature.asc Description: PGP signature
Re: [PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines
Hello Maxime, max...@cerno.tech wrote on Sun, 18 Jun 2023 16:37:58 +0200: > Hi, > > On Fri, Jun 16, 2023 at 06:32:51PM +0200, Miquel Raynal wrote: > > The ST7789V LCD controller supports regular SPI wiring, as well as no Rx > > data line at all. The operating system needs to know whether it can read > > registers from the device or not. Let's detail this specific design > > possibility by bounding the spi-rx-bus-width property. > > > > Signed-off-by: Miquel Raynal > > --- > > .../devicetree/bindings/display/panel/sitronix,st7789v.yaml | 4 > > 1 file changed, 4 insertions(+) > > > > diff --git > > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > index 0ccf0487fd8e..a25df7e1df88 100644 > > --- a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > +++ b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > > @@ -29,6 +29,10 @@ properties: > >spi-cpha: true > >spi-cpol: true > > > > + spi-rx-bus-width: > > +minimum: 0 > > +maximum: 1 > > + > > It's not clear to me what the default would be? This binding references spi-peripheral-props.yaml which sets the default to 1, I believe it is sane to keep it that way? Thanks, Miquèl
Re: [PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines
Hi, On Fri, Jun 16, 2023 at 06:32:51PM +0200, Miquel Raynal wrote: > The ST7789V LCD controller supports regular SPI wiring, as well as no Rx > data line at all. The operating system needs to know whether it can read > registers from the device or not. Let's detail this specific design > possibility by bounding the spi-rx-bus-width property. > > Signed-off-by: Miquel Raynal > --- > .../devicetree/bindings/display/panel/sitronix,st7789v.yaml | 4 > 1 file changed, 4 insertions(+) > > diff --git > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > index 0ccf0487fd8e..a25df7e1df88 100644 > --- a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > +++ b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > @@ -29,6 +29,10 @@ properties: >spi-cpha: true >spi-cpol: true > > + spi-rx-bus-width: > +minimum: 0 > +maximum: 1 > + It's not clear to me what the default would be? Maxime signature.asc Description: PGP signature
Re: [PATCH v2 2/6] dt-bindings: display: st7789v: bound the number of Rx data lines
On 16/06/2023 18:32, Miquel Raynal wrote: > The ST7789V LCD controller supports regular SPI wiring, as well as no Rx > data line at all. The operating system needs to know whether it can read > registers from the device or not. Let's detail this specific design > possibility by bounding the spi-rx-bus-width property. > > Signed-off-by: Miquel Raynal > --- > .../devicetree/bindings/display/panel/sitronix,st7789v.yaml | 4 > 1 file changed, 4 insertions(+) > > diff --git > a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > index 0ccf0487fd8e..a25df7e1df88 100644 > --- a/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > +++ b/Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml > @@ -29,6 +29,10 @@ properties: >spi-cpha: true >spi-cpol: true > > + spi-rx-bus-width: > +minimum: 0 > +maximum: 1 0 is already minimum, but I understand you want to emphasize lack of RX. Acked-by: Krzysztof Kozlowski Best regards, Krzysztof
