[PATCH v2 0/2] serial: 8250_dw: fall back to poll if there's no interrupt

[PATCH v2 0/2] serial: 8250_dw: fall back to poll if there's no interrupt

[Jisheng Zhang]

When there's no irq(this can be due to various reasons, for example,
no irq from HW support, or we just want to use poll solution, and so
on), falling back to poll is still better than no support at all.

patch1 makes the interrupt property in dt-binding optional
patch2 falls back to poll if there's no interrupt

since v1:
 - adopt Andy's suggestion to simplified the code

Jisheng Zhang (2):
  dt-bindings: serial: snps-dw-apb-uart: make interrupt optional
  serial: 8250_dw: fall back to poll if there's no interrupt

 .../devicetree/bindings/serial/snps-dw-apb-uart.yaml         | 1 -
 drivers/tty/serial/8250/8250_dw.c                            | 5 ++++-
 2 files changed, 4 insertions(+), 2 deletions(-)

-- 
2.40.1

[PATCH v2 1/2] dt-bindings: serial: snps-dw-apb-uart: make interrupt optional

[Jisheng Zhang]

The driver fall back to poll style when there's no irq. "poll" still
looks better than no support.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
index 3862411c77b5..17c553123f96 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
@@ -117,7 +117,6 @@ properties:
 required:
   - compatible
   - reg
-  - interrupts
 
 unevaluatedProperties: false
 
-- 
2.40.1

[PATCH v2 2/2] serial: 8250_dw: fall back to poll if there's no interrupt

[Jisheng Zhang]

When there's no irq(this can be due to various reasons, for example,
no irq from HW support, or we just want to use poll solution, and so
on), falling back to poll is still better than no support at all.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 drivers/tty/serial/8250/8250_dw.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 7db51781289e..f4cafca1a7da 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -523,7 +523,10 @@ static int dw8250_probe(struct platform_device *pdev)
 	if (!regs)
 		return dev_err_probe(dev, -EINVAL, "no registers defined\n");
 
-	irq = platform_get_irq(pdev, 0);
+	irq = platform_get_irq_optional(pdev, 0);
+	/* no interrupt -> fall back to polling */
+	if (irq == -ENXIO)
+		irq = 0;
 	if (irq < 0)
 		return irq;
 
-- 
2.40.1

Re: [PATCH v2 0/2] serial: 8250_dw: fall back to poll if there's no interrupt

[Jisheng Zhang]

On Sun, Aug 06, 2023 at 12:20:11PM +0200, Greg Kroah-Hartman wrote:
> On Sun, Aug 06, 2023 at 05:20:54PM +0800, Jisheng Zhang wrote:
> > When there's no irq(this can be due to various reasons, for example,
> > no irq from HW support, or we just want to use poll solution, and so
> > on), falling back to poll is still better than no support at all.
> 
> Ouch, really?  Why not just fix the hardware instead?
> 

Hi Greg,

The HW may be designed as that to save interrupt lines if the uart
is dedicated to debug purpose. I also see similar support in other
uart drivers, for example liteuart.c, altera_uart.c, altera_jtaguart.c
8250_ioc3.c and so on.

Thanks

Re: [PATCH v2 0/2] serial: 8250_dw: fall back to poll if there's no interrupt

[Greg Kroah-Hartman]

On Sun, Aug 06, 2023 at 05:20:54PM +0800, Jisheng Zhang wrote:
> When there's no irq(this can be due to various reasons, for example,
> no irq from HW support, or we just want to use poll solution, and so
> on), falling back to poll is still better than no support at all.

Ouch, really?  Why not just fix the hardware instead?

Re: [PATCH v2 1/2] dt-bindings: serial: snps-dw-apb-uart: make interrupt optional

[Rob Herring]

On Sun, 06 Aug 2023 17:20:55 +0800, Jisheng Zhang wrote:
> The driver fall back to poll style when there's no irq. "poll" still
> looks better than no support.
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml | 1 -
>  1 file changed, 1 deletion(-)
> 

Reviewed-by: Rob Herring <robh@kernel.org>