From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp5.netcologne.de (smtp5.netcologne.de [194.8.194.25]) by ozlabs.org (Postfix) with ESMTP id 375DEB7CC2 for ; Thu, 4 Mar 2010 05:23:07 +1100 (EST) Date: Wed, 03 Mar 2010 19:23:03 +0100 From: Albrecht =?iso-8859-1?b?RHJl3w==?= Subject: [Patch v.2] mpc5200b/uart: improve baud rate calculation (reach high baud rates, better accuracy) To: Linux PPC Development , "Likely, Grant" Message-Id: <1267640583.4760.0@antares> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On the MPC5200B, make very high baud rates (e.g. 3 MBaud) accessible and achieve a higher precision for high baud rates in general. This is done by selecting the appropriate prescaler (/4 or /32). As to keep the code clean= , the getuartclk method has been dropped, and all calculations are done with = a "virtual" /4 prescaler for all chips for maximum accuracy. A new set_divis= or method scales down the divisor values found by the generic serial code appropriately. Note: only "fsl,mpc5200b-psc-uart" compatible devices benefit from these improvements. Tested on a custom 5200B based board, with up to 3 MBaud, and with both "fsl,mpc5200b-psc-uart" and "fsl,mpc5200-psc-uart" devices. Signed-off-by: Albrecht Dre=DF --- Changes vs. v.1: include improvements suggested by Wolfram and Grant (thank= s a lot for your helpful input!!): drop getuartclk method and use the highest possible frequency for calculation, use new psc_ops for the 5200b, let the set_divisor method do all the dirty work, emit warnings if bad divisor valu= es have been selected. =20 --- linux-2.6.33-orig/drivers/serial/mpc52xx_uart.c 2010-02-24 19:52:17.000= 000000 +0100 +++ linux-2.6.33/drivers/serial/mpc52xx_uart.c 2010-03-03 10:52:04.00000000= 0 +0100 @@ -144,7 +144,8 @@ struct psc_ops { unsigned char (*read_char)(struct uart_port *port); void (*cw_disable_ints)(struct uart_port *port); void (*cw_restore_ints)(struct uart_port *port); - unsigned long (*getuartclk)(void *p); + void (*set_divisor)(struct uart_port *port, + unsigned int divisor); }; =20 #ifdef CONFIG_PPC_MPC52xx @@ -154,9 +155,6 @@ static void mpc52xx_psc_fifo_init(struct struct mpc52xx_psc __iomem *psc =3D PSC(port); struct mpc52xx_psc_fifo __iomem *fifo =3D FIFO_52xx(port); =20 - /* /32 prescaler */ - out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); - out_8(&fifo->rfcntl, 0x00); out_be16(&fifo->rfalarm, 0x1ff); out_8(&fifo->tfcntl, 0x07); @@ -245,15 +243,55 @@ static void mpc52xx_psc_cw_restore_ints( out_be16(&PSC(port)->mpc52xx_psc_imr, port->read_status_mask); } =20 -/* Search for bus-frequency property in this node or a parent */ -static unsigned long mpc52xx_getuartclk(void *p) +static void mpc52xx_psc_set_divisor(struct uart_port *port, + unsigned int divisor) { - /* - * 5200 UARTs have a / 32 prescaler - * but the generic serial code assumes 16 - * so return ipb freq / 2 - */ - return mpc5xxx_get_bus_frequency(p) / 2; + struct mpc52xx_psc __iomem *psc =3D PSC(port); + + /* adjust divisor for a /32 prescaler; see note in + * mpc52xx_uart_of_probe() */ + divisor =3D (divisor + 4) / 8; + if (divisor > 0xffff) { + pr_warning("%s: divisor overflow (%x), use 0xffff\n", __func__, + divisor); + divisor =3D 0xffff; + } else if (divisor =3D=3D 0) { + pr_warning("%s: divisor 0, use 1\n", __func__); + divisor =3D 1; + } + + /* prescaler */ + out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); /* /32 */ + + /* ctr */ + out_8(&psc->ctur, divisor >> 8); + out_8(&psc->ctlr, divisor & 0xff); +} + +static void mpc5200b_psc_set_divisor(struct uart_port *port, + unsigned int divisor) +{ + struct mpc52xx_psc __iomem *psc =3D PSC(port); + + /* set prescaler; see note in mpc52xx_uart_of_probe() */ + if (divisor > 0xffff) { + divisor =3D (divisor + 4) / 8; + out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); /* /32 */ + } else + out_be16(&psc->mpc52xx_psc_clock_select, 0xff00); /* /4 */ + + if (divisor > 0xffff) { + pr_warning("%s: divisor overflow (%x), use 0xffff\n", __func__, + divisor); + divisor =3D 0xffff; + } else if (divisor =3D=3D 0) { + pr_warning("%s: divisor 0, use 1\n", __func__); + divisor =3D 1; + } + + /* ctr */ + out_8(&psc->ctur, divisor >> 8); + out_8(&psc->ctlr, divisor & 0xff); } =20 static struct psc_ops mpc52xx_psc_ops =3D { @@ -272,7 +310,26 @@ static struct psc_ops mpc52xx_psc_ops =3D=20 .read_char =3D mpc52xx_psc_read_char, .cw_disable_ints =3D mpc52xx_psc_cw_disable_ints, .cw_restore_ints =3D mpc52xx_psc_cw_restore_ints, - .getuartclk =3D mpc52xx_getuartclk, + .set_divisor =3D mpc52xx_psc_set_divisor, +}; + +static struct psc_ops mpc5200b_psc_ops =3D { + .fifo_init =3D mpc52xx_psc_fifo_init, + .raw_rx_rdy =3D mpc52xx_psc_raw_rx_rdy, + .raw_tx_rdy =3D mpc52xx_psc_raw_tx_rdy, + .rx_rdy =3D mpc52xx_psc_rx_rdy, + .tx_rdy =3D mpc52xx_psc_tx_rdy, + .tx_empty =3D mpc52xx_psc_tx_empty, + .stop_rx =3D mpc52xx_psc_stop_rx, + .start_tx =3D mpc52xx_psc_start_tx, + .stop_tx =3D mpc52xx_psc_stop_tx, + .rx_clr_irq =3D mpc52xx_psc_rx_clr_irq, + .tx_clr_irq =3D mpc52xx_psc_tx_clr_irq, + .write_char =3D mpc52xx_psc_write_char, + .read_char =3D mpc52xx_psc_read_char, + .cw_disable_ints =3D mpc52xx_psc_cw_disable_ints, + .cw_restore_ints =3D mpc52xx_psc_cw_restore_ints, + .set_divisor =3D mpc5200b_psc_set_divisor, }; =20 #endif /* CONFIG_MPC52xx */ @@ -388,9 +445,25 @@ static void mpc512x_psc_cw_restore_ints( out_be32(&FIFO_512x(port)->rximr, port->read_status_mask & 0x7f); } =20 -static unsigned long mpc512x_getuartclk(void *p) +static void mpc512x_psc_set_divisor(struct uart_port *port, + unsigned int divisor) { - return mpc5xxx_get_bus_frequency(p); + struct mpc52xx_psc __iomem *psc =3D PSC(port); + + /* adjust divisor for a /16 prescaler; see note in + * mpc52xx_uart_of_probe() */ + divisor =3D (divisor + 2) / 4; + if (divisor > 0xffff) { + pr_warning("%s: divisor overflow (%x), use 0xffff\n", __func__, + divisor); + divisor =3D 0xffff; + } else if (divisor =3D=3D 0) { + pr_warning("%s: divisor 0, use 1\n", __func__); + divisor =3D 1; + } + + out_8(&psc->ctur, divisor >> 8); + out_8(&psc->ctlr, divisor & 0xff); } =20 static struct psc_ops mpc512x_psc_ops =3D { @@ -409,7 +482,7 @@ static struct psc_ops mpc512x_psc_ops =3D=20 .read_char =3D mpc512x_psc_read_char, .cw_disable_ints =3D mpc512x_psc_cw_disable_ints, .cw_restore_ints =3D mpc512x_psc_cw_restore_ints, - .getuartclk =3D mpc512x_getuartclk, + .set_divisor =3D mpc512x_psc_set_divisor, }; #endif =20 @@ -564,7 +637,6 @@ mpc52xx_uart_set_termios(struct uart_por struct mpc52xx_psc __iomem *psc =3D PSC(port); unsigned long flags; unsigned char mr1, mr2; - unsigned short ctr; unsigned int j, baud, quot; =20 /* Prepare what we're gonna write */ @@ -604,7 +676,6 @@ mpc52xx_uart_set_termios(struct uart_por =20 baud =3D uart_get_baud_rate(port, new, old, 0, port->uartclk/16); quot =3D uart_get_divisor(port, baud); - ctr =3D quot & 0xffff; =20 /* Get the lock */ spin_lock_irqsave(&port->lock, flags); @@ -635,8 +706,7 @@ mpc52xx_uart_set_termios(struct uart_por out_8(&psc->command, MPC52xx_PSC_SEL_MODE_REG_1); out_8(&psc->mode, mr1); out_8(&psc->mode, mr2); - out_8(&psc->ctur, ctr >> 8); - out_8(&psc->ctlr, ctr & 0xff); + psc_ops->set_divisor(port, quot); =20 if (UART_ENABLE_MS(port, new->c_cflag)) mpc52xx_uart_enable_ms(port); @@ -1007,7 +1077,8 @@ mpc52xx_console_setup(struct console *co return ret; } =20 - uartclk =3D psc_ops->getuartclk(np); + /* see remarks about the uart clock in mpc52xx_uart_of_probe() */ + uartclk =3D mpc5xxx_get_bus_frequency(np) * 4; if (uartclk =3D=3D 0) { pr_debug("Could not find uart clock frequency!\n"); return -EINVAL; @@ -1090,6 +1161,7 @@ static struct uart_driver mpc52xx_uart_d =20 static struct of_device_id mpc52xx_uart_of_match[] =3D { #ifdef CONFIG_PPC_MPC52xx + { .compatible =3D "fsl,mpc5200b-psc-uart", .data =3D &mpc5200b_psc_ops, }= , { .compatible =3D "fsl,mpc5200-psc-uart", .data =3D &mpc52xx_psc_ops, }, /* binding used by old lite5200 device trees: */ { .compatible =3D "mpc5200-psc-uart", .data =3D &mpc52xx_psc_ops, }, @@ -1122,7 +1194,24 @@ mpc52xx_uart_of_probe(struct of_device * pr_debug("Found %s assigned to ttyPSC%x\n", mpc52xx_uart_nodes[idx]->full_name, idx); =20 - uartclk =3D psc_ops->getuartclk(op->node); + /* + * Note about the uart clock: + * This series of processors use the ipb clock frequency for the clock + * generation scaled down by prescalers and a 16-bit counter register: + * - the 5200 has a /32 prescaler + * - the 5200B has selectable /4 or /32 prescalers (i.e. the counter + * reg can be viewed as a 19-bit value, of which we can use either + * the upper or the lower 16 bits - in the latter case the three + * MSB's must of course be 0) + * - the 512x has a /16 prescaler + * The generic serial code assumes a prescaler of /16. As we want to + * achieve the maximum accuracy possible, we let the generic serial + * code perform all calculations with the /4 prescaler, i.e. we have + * to set the uart clock to ipb freq * 4 here. The set_divisor methods + * for the different chips are responsible for scaling down the divisor + * value appropriately. + */ + uartclk =3D mpc5xxx_get_bus_frequency(op->node) * 4; if (uartclk =3D=3D 0) { dev_dbg(&op->dev, "Could not find uart clock frequency!\n"); return -EINVAL;