linux-kernel - Re: [PATCH 1/3] serial: qcom-geni: fix hard lockup on buffer flush

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Date: Tue, 25 Jun 2024 09:27:01 -0700
From: Doug Anderson <dianders@...omium.org>
To: Johan Hovold <johan@...nel.org>
Cc: Johan Hovold <johan+linaro@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Bjorn Andersson <andersson@...nel.org>, 
	linux-arm-msm@...r.kernel.org, linux-serial@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] serial: qcom-geni: fix hard lockup on buffer flush

Hi,

On Tue, Jun 25, 2024 at 7:53 AM Johan Hovold <johan@...nel.org> wrote:
>
> On Mon, Jun 24, 2024 at 01:45:17PM -0700, Doug Anderson wrote:
>
> > Also: if we're looking at quick/easy to land and just fix the hard
> > lockup, I'd vote for this (I can send a real patch, though I'm about
> > to go on vacation):
> >
> > --
> >
> > @@ -904,8 +904,8 @@ static void qcom_geni_serial_handle_tx_fifo(struct
> > uart_port *uport,
> >                 goto out_write_wakeup;
> >
> >         if (!port->tx_remaining) {
> > -               qcom_geni_serial_setup_tx(uport, pending);
> > -               port->tx_remaining = pending;
> > +               port->tx_remaining = min(avail, pending);
> > +               qcom_geni_serial_setup_tx(uport, port->tx_remaining);
> >
> >                 irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
> >                 if (!(irq_en & M_TX_FIFO_WATERMARK_EN))
> >
> > --
> >
> > That will fix the hard lockup, is short and sweet, and also doesn't
> > end up outputting NUL bytes.
>
> Yeah, this might be a good stop gap even if performance suffers.

I've officially posted this as:

https://lore.kernel.org/r/20240625092440.1.Icf914852be911b95aefa9d798b6f1cd1a180f985@changeid

I realized that I didn't need to re-calculate "chunk" so the patch is
very slightly different than I posted above but should be effectively
the same.

-Doug