From: Arnd Bergmann <arnd@arndb.de>
To: "Subhasish Ghosh" <subhasish@mistralsolutions.com>
Subject: Re: [PATCH v2 13/13] tty: pruss SUART driver
Date: Tue, 22 Feb 2011 17:34:15 +0100
User-Agent: KMail/1.12.2 (Linux/2.6.31-22-generic; KDE/4.3.2; x86_64; ; )
Cc: linux-arm-kernel@lists.infradead.org,
        "Thomas Gleixner" <tglx@linutronix.de>,
        "Alan Cox" <alan@lxorguk.ukuu.org.uk>, sachi@mistralsolutions.com,
        davinci-linux-open-source@linux.davincidsp.com,
        "Greg Kroah-Hartman" <gregkh@suse.de>, nsekhar@ti.com,
        "open list" <linux-kernel@vger.kernel.org>, m-watkins@ti.com
References: <1297435892-28278-1-git-send-email-subhasish@mistralsolutions.com> <201102181951.32631.arnd@arndb.de> <DADE3366197E4479A57F3B967A881C33@subhasishg>
In-Reply-To: <DADE3366197E4479A57F3B967A881C33@subhasishg>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <201102221734.15582.arnd@arndb.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2199
Lines: 52

On Tuesday 22 February 2011, Subhasish Ghosh wrote:

> @@ -122,13 +122,10 @@ static void omapl_pru_tx_chars(struct omapl_pru_suart 
> *soft_uart, u32 uart_no)
>         if (!(suart_get_duplex(soft_uart, uart_no) & ePRU_SUART_HALF_TX))
>                 return;
> 
> -       if (down_trylock(&soft_uart->port_sem[uart_no]))
> -               return;
> -
>         if (uart_circ_empty(xmit) ||
>                         uart_tx_stopped(&soft_uart->port[uart_no])) {
>                 pruss_suart_stop_tx(&soft_uart->port[uart_no]);
> -               up(&soft_uart->port_sem[uart_no]);
> +               soft_uart->tx_empty[uart_no] = true;
>                 return;
>         }
> 
> @@ -259,7 +256,6 @@ static irqreturn_t pruss_suart_interrupt(s32 irq, void 
> *dev_id)
>                         pru_intr_clr_isrstatus(dev, uart_num, PRU_TX_INTR);
>                         pru_softuart_clr_tx_status(dev, &soft_uart->suart_hdl
>                                                  [port->line]);
> -                       up(&soft_uart->port_sem[port->line]);
>                         omapl_pru_tx_chars(soft_uart, port->line);
>                 }
>         } while (txrx_flag & (PRU_RX_INTR | PRU_TX_INTR));
> @@ -294,7 +290,10 @@ static void pruss_suart_start_tx(struct uart_port 
> *port)
> 
>         suart_intr_setmask(dev, soft_uart->suart_hdl[port->line].uart_num,
>                            PRU_TX_INTR, CHN_TXRX_IE_MASK_CMPLT);
> -       omapl_pru_tx_chars(soft_uart, port->line);
> +       if (soft_uart->tx_empty[port->line] == true) {
> +               soft_uart->tx_empty[port->line] = false;
> +               omapl_pru_tx_chars(soft_uart, port->line);
> +       }
>  }

This looks racy, and I think you at least need to take the spinlock in
pruss_suart_start_tx(), but I don't fully understand the intention of the
code.

I guess you could also use a bitmask for tx_empty and use test_and_clear_bit()
on that to guarantee atomicity.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/