linux-kernel - Re: [PATCH v4 8/8] serial: qcom-geni: Rework TX in FIFO mode to fix hangs/lockups

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Date: Mon, 17 Jun 2024 21:10:07 +0200
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Douglas Anderson <dianders@...omium.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>
Cc: Yicong Yang <yangyicong@...ilicon.com>, Tony Lindgren <tony@...mide.com>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Johan Hovold <johan+linaro@...nel.org>,
 John Ogness <john.ogness@...utronix.de>, linux-arm-msm@...r.kernel.org,
 Bjorn Andersson <andersson@...nel.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Stephen Boyd <swboyd@...omium.org>, linux-serial@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
 Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v4 8/8] serial: qcom-geni: Rework TX in FIFO mode to fix
 hangs/lockups



On 6/11/24 00:24, Douglas Anderson wrote:
> The fact that the Qualcomm GENI hardware interface is based around
> "packets" is really awkward to fit into Linux's UART design.
> Specifically, in order to send bytes you need to start up a new
> "command" saying how many bytes you want to send and then you need to
> send all those bytes. Once you've committed to sending that number of
> bytes it's very awkward to change your mind and send fewer, especially
> if you want to do so without dropping bytes on the ground.

[...]

  
> +static void qcom_geni_serial_enable_cmd_done(struct uart_port *uport)
> +{
> +	struct qcom_geni_serial_port *port = to_dev_port(uport);
> +
> +	/* If we're not in FIFO mode we don't use CMD_DONE. */
> +	if (port->dev_data->mode != GENI_SE_FIFO)
> +		return;
> +
> +	writel(M_CMD_DONE_EN, uport->membase + SE_GENI_M_IRQ_EN_SET);
> +}

IDK if this is worth of a separate function, instead of checking for the
FIFO in port_setup and writing it there, but generally this patch looks
good to me

Reviewed-by: Konrad Dybcio <konrad.dybcio@...aro.org>

Konrad