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

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Message-ID: <b7b04cb8-03cb-4175-8575-b56004e65775@linaro.org>
Date: Mon, 17 Jun 2024 21:54:39 +0200
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Doug Anderson <dianders@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>, 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 6/17/24 21:37, Doug Anderson wrote:
> Hi,
> 
> On Mon, Jun 17, 2024 at 12:10 PM Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
>>
>>
>>
>> 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
> 
> Sure. Somehow it felt weird to me to put it straight in there, but I
> could go either way. Do you think I should spin the series just for
> this, or just make this change if I happen to need to spin the series
> for something else?

The latter.

Konrad