linux-kernel - Re: [External Email] Re: [PATCH v2 1/2] dt-bindings: serial: sc16is7xx: Add description for polling mode

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Message-ID: <5582697e-bbf1-9a35-c5a4-52f09fdc6067@systec-electronic.com>
Date: Tue, 7 Jan 2025 09:49:28 +0100 (CET)
From: Andre Werner <andre.werner@...tec-electronic.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
cc: Andre Werner <andre.werner@...tec-electronic.com>, 
    gregkh@...uxfoundation.org, jirislaby@...nel.org, hvilleneuve@...onoff.com, 
    andy@...nel.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
    linux-serial@...r.kernel.org, lech.perczak@...lingroup.com, 
    krzk+dt@...nel.org, conor+dt@...nel.org, robh@...nel.org
Subject: Re: [External Email] Re: [PATCH v2 1/2] dt-bindings: serial: sc16is7xx:
 Add description for polling mode

Dear Krzysztof,

On Tue, 7 Jan 2025, Krzysztof Kozlowski wrote:

> On Mon, Jan 06, 2025 at 09:50:50AM +0100, Andre Werner wrote:
> > Polling mode is enabled if the "interrupts" property is missing.
> > Thus, this commit deletes "interrupts" entry from "required" section
> > and adds a description for the fallback to polling mode at the
> > "interrupts" entry.
>
> Can the device actually operate with interrupt line disconnected? I
> skimmed through datasheet and they did not mention that as a valid
> setup.

For polling mode the datasheet said:

In Polled mode (IER[3:0] = 0000) the status of the receiver and transmitter can be
checked by polling the Line Status Register (LSR). This mode is an alternative to the FIFO
Interrupt mode of operation where the status of the receiver and transmitter is
automatically known by means of interrupts sent to the CPU.

This is what the driver does. It polls the LSR according to poll period
used in the driver. Unfortunately, the internal TX and especially RX
buffer is very small. So we need to poll in a very short period.

>
> Best regards,
> Krzysztof
>
>

Regards,

Andre