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

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Date:   Sun, 6 Aug 2023 17:40:27 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Conor Dooley <conor@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: serial: snps-dw-apb-uart: make
 interrupt optional

On Thu, Aug 03, 2023 at 02:40:05PM +0300, Andy Shevchenko wrote:
> On Wed, Aug 02, 2023 at 11:53:59PM +0100, Conor Dooley wrote:
> > On Thu, Aug 03, 2023 at 12:57:44AM +0300, Andy Shevchenko wrote:
> > > On Wed, Aug 02, 2023 at 04:43:48PM +0100, Conor Dooley wrote:
> > > > On Wed, Aug 02, 2023 at 11:05:44PM +0800, Jisheng Zhang wrote:
> > > > > The driver fall back to poll style when there's no irq. "poll" still
> > > > > looks better than no support.
> > > > 
> > > > What is the user for this where the interrupt is not actually wired up
> > > > in the hardware?
> > > 
> > > FYI: kernel console doesn't use interrupts, so for example it might be
> > > the debug port. Note, I have no idea of the Zhang's case, just my assumption.

Hi Conor, Andy,

Andy's assumption about the uart dedicated for debug purpose is true, since
it's for log only, so no interrupt need at all. We can also see such no
irq support in litex uart driver(liteuart.c) and even a 8250
variant(8250_ioc3.c).

Thanks
> > 
> > I'm less interested in what the software is doing, it's what the device 
> > that has not connected the interrupt is that I am curious about.
> 
> As I said. The hw may be purely for debugging purposes (and yes, I have heard
> about such a hardware).
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>