linux-kernel - Re: [PATCH v3 13/13] tty: serial: qcom-geni-serial: add support for serial engine DMA

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Message-ID: <CAMRc=Mdo-a3sxaTg=AM_dMMNyV_sw9VxGF-T5RPD2Vhxe2pQOw@mail.gmail.com>
Date:   Tue, 29 Nov 2022 11:13:23 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Vinod Koul <vkoul@...nel.org>, Alex Elder <elder@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-serial@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 13/13] tty: serial: qcom-geni-serial: add support for
 serial engine DMA

On Fri, Nov 25, 2022 at 3:37 PM Srinivas Kandagatla
<srinivas.kandagatla@...aro.org> wrote:
>

[snip]

> > +
> > +static void qcom_geni_serial_start_tx_dma(struct uart_port *uport)
> > +{
> > +     struct qcom_geni_serial_port *port = to_dev_port(uport);
> > +     struct circ_buf *xmit = &uport->state->xmit;
> > +     unsigned int xmit_size;
> > +     int ret;
> > +
> > +     if (port->tx_dma_addr)
> > +             return;
> Is this condition actually possible?
>

So it turns out, it's possible that the subsystem calls start_tx when
this is already set but the main engine is not yet in active state (so
we can't simply test that bit). This needs to stay then.

Bart