[PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Francesco Lavra]

This driver runs also on SoCs without a Tegra20 APB DMA controller (e.g.
Tegra234).
Remove the Kconfig dependency on TEGRA20_APB_DMA, and remove reference to
the APB DMA controller from the Kconfig help text.

Fixes: 60d2016a5161 ("arm64: tegra: Add Tegra234 GPCDMA device tree node")
Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 drivers/tty/serial/Kconfig | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 44427415a80d..6212a814fdb7 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -255,14 +255,13 @@ config SERIAL_SAMSUNG_CONSOLE
 
 config SERIAL_TEGRA
 	tristate "NVIDIA Tegra20/30 SoC serial controller"
-	depends on (ARCH_TEGRA && TEGRA20_APB_DMA) || COMPILE_TEST
+	depends on ARCH_TEGRA || COMPILE_TEST
 	select SERIAL_CORE
 	help
 	  Support for the on-chip UARTs on the NVIDIA Tegra series SOCs
 	  providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some machines may not
 	  provide all of these ports, depending on how the serial port
-	  are enabled). This driver uses the APB DMA to achieve higher baudrate
-	  and better performance.
+	  are enabled).
 
 config SERIAL_TEGRA_TCU
 	tristate "NVIDIA Tegra Combined UART"
-- 
2.39.5

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Andy Shevchenko]

On Wed, Nov 26, 2025 at 10:07:59AM +0100, Francesco Lavra wrote:
> This driver runs also on SoCs without a Tegra20 APB DMA controller (e.g.
> Tegra234).
> Remove the Kconfig dependency on TEGRA20_APB_DMA, and remove reference to
> the APB DMA controller from the Kconfig help text.

...

>  	help
>  	  Support for the on-chip UARTs on the NVIDIA Tegra series SOCs
>  	  providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some machines may not
>  	  provide all of these ports, depending on how the serial port
> -	  are enabled). This driver uses the APB DMA to achieve higher baudrate
> -	  and better performance.
> +	  are enabled).

I think this removes a good piece of information. Perhaps rephrase?

	  This driver may use the APB DMA when available to achieve
	  higher baudrate and better performance.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Francesco Lavra]

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On Wed, 2025-11-26 at 13:20 +0200, Andy Shevchenko wrote:
> On Wed, Nov 26, 2025 at 10:07:59AM +0100, Francesco Lavra wrote:
> > This driver runs also on SoCs without a Tegra20 APB DMA controller
> > (e.g.
> > Tegra234).
> > Remove the Kconfig dependency on TEGRA20_APB_DMA, and remove reference
> > to
> > the APB DMA controller from the Kconfig help text.
> 
> ...
> 
> >         help
> >           Support for the on-chip UARTs on the NVIDIA Tegra series SOCs
> >           providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some machines
> > may not
> >           provide all of these ports, depending on how the serial port
> > -         are enabled). This driver uses the APB DMA to achieve higher
> > baudrate
> > -         and better performance.
> > +         are enabled).
> 
> I think this removes a good piece of information. Perhaps rephrase?
> 
>           This driver may use the APB DMA when available to achieve
>           higher baudrate and better performance.

I think this sentence would make it sound like the driver performs better
if the APB DMA controller is available, but in reality the driver just uses
the generic DMA API like most serial drivers, and there is nothing APB-
specific in it. If another DMA controller (e.g. GPC on Tegra234) is
available instead of the APB one, the serial peripheral will be just as
fast.

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Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Andy Shevchenko]

On Wed, Nov 26, 2025 at 01:08:23PM +0100, Francesco Lavra wrote:
> On Wed, 2025-11-26 at 13:20 +0200, Andy Shevchenko wrote:
> > On Wed, Nov 26, 2025 at 10:07:59AM +0100, Francesco Lavra wrote:

...

> > >         help
> > >           Support for the on-chip UARTs on the NVIDIA Tegra series SOCs
> > >           providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some machines
> > > may not
> > >           provide all of these ports, depending on how the serial port
> > > -         are enabled). This driver uses the APB DMA to achieve higher
> > > baudrate
> > > -         and better performance.
> > > +         are enabled).
> > 
> > I think this removes a good piece of information. Perhaps rephrase?
> > 
> >           This driver may use the APB DMA when available to achieve
> >           higher baudrate and better performance.
> 
> I think this sentence would make it sound like the driver performs better
> if the APB DMA controller is available, but in reality the driver just uses
> the generic DMA API like most serial drivers, and there is nothing APB-
> specific in it. If another DMA controller (e.g. GPC on Tegra234) is
> available instead of the APB one, the serial peripheral will be just as
> fast.

OK. But this is not the case for Tegra234? Or is it and it uses DMA for UART?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Francesco Lavra]

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On Wed, 2025-11-26 at 18:25 +0200, Andy Shevchenko wrote:
> On Wed, Nov 26, 2025 at 01:08:23PM +0100, Francesco Lavra wrote:
> > On Wed, 2025-11-26 at 13:20 +0200, Andy Shevchenko wrote:
> > > On Wed, Nov 26, 2025 at 10:07:59AM +0100, Francesco Lavra wrote:
> 
> ...
> 
> > > >         help
> > > >           Support for the on-chip UARTs on the NVIDIA Tegra series
> > > > SOCs
> > > >           providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some
> > > > machines
> > > > may not
> > > >           provide all of these ports, depending on how the serial
> > > > port
> > > > -         are enabled). This driver uses the APB DMA to achieve
> > > > higher
> > > > baudrate
> > > > -         and better performance.
> > > > +         are enabled).
> > > 
> > > I think this removes a good piece of information. Perhaps rephrase?
> > > 
> > >           This driver may use the APB DMA when available to achieve
> > >           higher baudrate and better performance.
> > 
> > I think this sentence would make it sound like the driver performs
> > better
> > if the APB DMA controller is available, but in reality the driver just
> > uses
> > the generic DMA API like most serial drivers, and there is nothing APB-
> > specific in it. If another DMA controller (e.g. GPC on Tegra234) is
> > available instead of the APB one, the serial peripheral will be just as
> > fast.
> 
> OK. But this is not the case for Tegra234? Or is it and it uses DMA for
> UART?

Yes, that is the case, Tegra234 has just a different DMA controller
(TEGRA186_GPC_DMA), which is used by the UART driver as long as the
relevant device tree node properties are in place.

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Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Andy Shevchenko]

On Wed, Nov 26, 2025 at 05:45:25PM +0100, Francesco Lavra wrote:
> On Wed, 2025-11-26 at 18:25 +0200, Andy Shevchenko wrote:
> > On Wed, Nov 26, 2025 at 01:08:23PM +0100, Francesco Lavra wrote:
> > > On Wed, 2025-11-26 at 13:20 +0200, Andy Shevchenko wrote:
> > > > On Wed, Nov 26, 2025 at 10:07:59AM +0100, Francesco Lavra wrote:

...

> > > > >         help
> > > > >           Support for the on-chip UARTs on the NVIDIA Tegra series
> > > > > SOCs
> > > > >           providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some
> > > > > machines
> > > > > may not
> > > > >           provide all of these ports, depending on how the serial
> > > > > port
> > > > > -         are enabled). This driver uses the APB DMA to achieve
> > > > > higher
> > > > > baudrate
> > > > > -         and better performance.
> > > > > +         are enabled).
> > > > 
> > > > I think this removes a good piece of information. Perhaps rephrase?
> > > > 
> > > >           This driver may use the APB DMA when available to achieve
> > > >           higher baudrate and better performance.
> > > 
> > > I think this sentence would make it sound like the driver performs
> > > better
> > > if the APB DMA controller is available, but in reality the driver just
> > > uses
> > > the generic DMA API like most serial drivers, and there is nothing APB-
> > > specific in it. If another DMA controller (e.g. GPC on Tegra234) is
> > > available instead of the APB one, the serial peripheral will be just as
> > > fast.
> > 
> > OK. But this is not the case for Tegra234? Or is it and it uses DMA for
> > UART?
> 
> Yes, that is the case, Tegra234 has just a different DMA controller
> (TEGRA186_GPC_DMA), which is used by the UART driver as long as the
> relevant device tree node properties are in place.

Okay, with this it means that some generic statement like

           This driver may use the DMA when available to achieve
           higher baudrate and better performance.

is too generic to be added. That said, I agree that you dropped
the original one completely.

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>


-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Francesco Lavra]

Friendly ping

On Wed, 2025-11-26 at 10:07 +0100, Francesco Lavra wrote:
> This driver runs also on SoCs without a Tegra20 APB DMA controller (e.g.
> Tegra234).
> Remove the Kconfig dependency on TEGRA20_APB_DMA, and remove reference to
> the APB DMA controller from the Kconfig help text.
> 
> Fixes: 60d2016a5161 ("arm64: tegra: Add Tegra234 GPCDMA device tree
> node")
> Signed-off-by: Francesco Lavra <flavra@baylibre.com>
> ---
>  drivers/tty/serial/Kconfig | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 44427415a80d..6212a814fdb7 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -255,14 +255,13 @@ config SERIAL_SAMSUNG_CONSOLE
>  
>  config SERIAL_TEGRA
>         tristate "NVIDIA Tegra20/30 SoC serial controller"
> -       depends on (ARCH_TEGRA && TEGRA20_APB_DMA) || COMPILE_TEST
> +       depends on ARCH_TEGRA || COMPILE_TEST
>         select SERIAL_CORE
>         help
>           Support for the on-chip UARTs on the NVIDIA Tegra series SOCs
>           providing /dev/ttyTHS0, 1, 2, 3 and 4 (note, some machines may
> not
>           provide all of these ports, depending on how the serial port
> -         are enabled). This driver uses the APB DMA to achieve higher
> baudrate
> -         and better performance.
> +         are enabled).
>  
>  config SERIAL_TEGRA_TCU
>         tristate "NVIDIA Tegra Combined UART"

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Jon Hunter]

On 26/11/2025 09:07, Francesco Lavra wrote:
> This driver runs also on SoCs without a Tegra20 APB DMA controller (e.g.
> Tegra234).
> Remove the Kconfig dependency on TEGRA20_APB_DMA, and remove reference to
> the APB DMA controller from the Kconfig help text.
> 
> Fixes: 60d2016a5161 ("arm64: tegra: Add Tegra234 GPCDMA device tree node")

This patch looks fine, but I would drop the fixes tag. 	There are other 
earlier devices, such as Tegra186 that also use this. Also please CC 
linux-tegra@vger.kernel.org on these patches too. I know people try to 
limit the number of list copied, but we may miss this otherwise.

Thanks
Jon

-- 
nvpublic

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Greg Kroah-Hartman]

On Wed, Feb 25, 2026 at 12:35:53PM +0100, Francesco Lavra wrote:
> Friendly ping

Can you resend this, I don't have it around anymore, thanks.

greg k-h

Re: [PATCH] serial: tegra: remove Kconfig dependency on APB DMA controller

[Francesco Lavra]

On Thu, 2026-03-12 at 14:43 +0100, Greg Kroah-Hartman wrote:
> On Wed, Feb 25, 2026 at 12:35:53PM +0100, Francesco Lavra wrote:
> > Friendly ping
> 
> Can you resend this, I don't have it around anymore, thanks.

I saw that it has been applied to the tty-testing branch already (thanks!),
anyway for reference the last version of the patch can be found at
https://patch.msgid.link/20260303111438.2691799-1-flavra@baylibre.com