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SubjectRE: [PATCH 02/14] serial: tegra: add support to ignore read
Date
> -----Original Message-----
> From: linux-tegra-owner@vger.kernel.org <linux-tegra-
> owner@vger.kernel.org> On Behalf Of Thierry Reding
> Sent: Tuesday, August 13, 2019 3:12 PM
> To: Krishna Yarlagadda <kyarlagadda@nvidia.com>
> Cc: gregkh@linuxfoundation.org; robh+dt@kernel.org;
> mark.rutland@arm.com; Jonathan Hunter <jonathanh@nvidia.com>; Laxman
> Dewangan <ldewangan@nvidia.com>; jslaby@suse.com; linux-
> serial@vger.kernel.org; devicetree@vger.kernel.org; linux-
> tegra@vger.kernel.org; linux-kernel@vger.kernel.org; Shardar Mohammed
> <smohammed@nvidia.com>
> Subject: Re: [PATCH 02/14] serial: tegra: add support to ignore read
>
> On Mon, Aug 12, 2019 at 04:58:11PM +0530, Krishna Yarlagadda wrote:
> > From: Shardar Shariff Md <smohammed@nvidia.com>
> >
> > Add support to ignore read characters if CREAD flag is not set.
> >
> > Signed-off-by: Shardar Shariff Md <smohammed@nvidia.com>
> > Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
> > ---
> > drivers/tty/serial/serial-tegra.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/tty/serial/serial-tegra.c
> > b/drivers/tty/serial/serial-tegra.c
> > index 19f4c24..93d299e 100644
> > --- a/drivers/tty/serial/serial-tegra.c
> > +++ b/drivers/tty/serial/serial-tegra.c
> > @@ -542,6 +542,9 @@ static void tegra_uart_handle_rx_pio(struct
> tegra_uart_port *tup,
> > ch = (unsigned char) tegra_uart_read(tup, UART_RX);
> > tup->uport.icount.rx++;
> >
> > + if (tup->uport.ignore_status_mask & UART_LSR_DR)
> > + continue;
> > +
> > if (!uart_handle_sysrq_char(&tup->uport, ch) && tty)
> > tty_insert_flip_char(tty, ch, flag);
>
> Is it a good idea to ignore even sysrq characters if CREAD is not set?
> According to termios, CREAD enables the receiver, so technically if it isn't set
> you can't even receive sysrq characters. But I don't know if there are any
> rules regarding this.
>
> Is this the same way that other drivers work?
>
> Thierry
>
Looked into few drivers and sysrq characters are not ignored. This driver does
not support console driver. So this might not be needed.

KY
> > } while (1);
> > @@ -562,6 +565,10 @@ static void tegra_uart_copy_rx_to_tty(struct
> tegra_uart_port *tup,
> > dev_err(tup->uport.dev, "No tty port\n");
> > return;
> > }
> > +
> > + if (tup->uport.ignore_status_mask & UART_LSR_DR)
> > + return;
> > +
> > dma_sync_single_for_cpu(tup->uport.dev, tup->rx_dma_buf_phys,
> > TEGRA_UART_RX_DMA_BUFFER_SIZE,
> DMA_FROM_DEVICE);
> > copied = tty_insert_flip_string(tty, @@ -1190,6 +1197,11 @@ static
> > void tegra_uart_set_termios(struct uart_port *u,
> > tegra_uart_write(tup, tup->ier_shadow, UART_IER);
> > tegra_uart_read(tup, UART_IER);
> >
> > + tup->uport.ignore_status_mask = 0;
> > + /* Ignore all characters if CREAD is not set */
> > + if ((termios->c_cflag & CREAD) == 0)
> > + tup->uport.ignore_status_mask |= UART_LSR_DR;
> > +
> > spin_unlock_irqrestore(&u->lock, flags); }
> >
> > --
> > 2.7.4
> >

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