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Date:   Fri, 3 Aug 2018 10:50:06 +0200
From:   Ludovic Desroches <ludovic.desroches@microchip.com>
To:     Richard Genoud <richard.genoud@gmail.com>
CC:     <linux-serial@vger.kernel.org>, <linux-arch@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <gregkh@linuxfoundation.org>, <jslaby@suse.com>, <arnd@arndb.de>,
        <nicolas.ferre@microchip.com>, <alexandre.belloni@bootlin.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] tty/serial: atmel: add ISO7816 support
Message-ID: <20180803085006.flatcfifnnlelruw@M43218.corp.atmel.com>
Mail-Followup-To: Richard Genoud <richard.genoud@gmail.com>,
        linux-serial@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, gregkh@linuxfoundation.org,
        jslaby@suse.com, arnd@arndb.de, nicolas.ferre@microchip.com,
        alexandre.belloni@bootlin.com, linux-kernel@vger.kernel.org
References: <20180719084737.1490-1-ludovic.desroches@microchip.com>
 <20180719084737.1490-3-ludovic.desroches@microchip.com>
 <1353b166-c1d0-6be6-a873-a54d210869fd@sorico.fr>
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Hi Richard,

On Fri, Jul 27, 2018 at 04:39:17PM +0200, Richard Genoud wrote:
> Hi Ludovic,
> 
> On 19/07/2018 10:47, Ludovic Desroches wrote:
> > From: Nicolas Ferre <nicolas.ferre@microchip.com>
> > 
> > When mode is set in atmel_config_iso7816() we backup last RS232 mode
> > for coming back to this mode if requested.
> > Also allow setup of T=0 and T=1 parameter and basic support in set_termios
> > function as well.
> > Report NACK and ITER errors in irq handler.
> > 
> > Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
> > Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
> > ---
> >  drivers/tty/serial/atmel_serial.c | 170 +++++++++++++++++++++++++++++++++++---
> >  drivers/tty/serial/atmel_serial.h |   3 +-
> >  2 files changed, 162 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> > index 8e4428725848..cec958f1e7d4 100644
> > --- a/drivers/tty/serial/atmel_serial.c
> > +++ b/drivers/tty/serial/atmel_serial.c
> > @@ -34,6 +34,7 @@
> >  #include <linux/suspend.h>
> >  #include <linux/mm.h>
> >  
> > +#include <asm/div64.h>
> >  #include <asm/io.h>
> >  #include <asm/ioctls.h>
> >  
> > @@ -147,6 +148,8 @@ struct atmel_uart_port {
> >  	struct circ_buf		rx_ring;
> >  
> >  	struct mctrl_gpios	*gpios;
> > +	u32			backup_mode;	/* MR saved during iso7816 operations */
> > +	u32			backup_brgr;	/* BRGR saved during iso7816 operations */
> >  	unsigned int		tx_done_mask;
> >  	u32			fifo_size;
> >  	u32			rts_high;
> > @@ -362,6 +365,132 @@ static int atmel_config_rs485(struct uart_port *port,
> >  	return 0;
> >  }
> >  
> > +static unsigned int atmel_calc_cd(struct uart_port *port,
> > +				  struct serial_iso7816 *iso7816conf)
> > +{
> > +	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
> > +	unsigned int cd;
> > +	u64 mck_rate;
> > +
> > +	mck_rate = (u64)clk_get_rate(atmel_port->clk);
> > +	do_div(mck_rate, iso7816conf->clk);
> > +	cd = mck_rate;
> > +	return cd;
> > +}
> > +
> > +static unsigned int atmel_calc_fidi(struct uart_port *port,
> > +				    struct serial_iso7816 *iso7816conf)
> > +{
> > +	u64 fidi = 0;
> > +
> > +	if (iso7816conf->sc_fi && iso7816conf->sc_di) {
> > +		fidi = (u64)iso7816conf->sc_fi;
> > +		do_div(fidi, iso7816conf->sc_di);
> > +	}
> > +	return (u32)fidi;
> > +}
> > +
> > +/* Enable or disable the iso7816 support */
> > +/* Called with interrupts disabled */
> > +static int atmel_config_iso7816(struct uart_port *port,
> > +				struct serial_iso7816 *iso7816conf)
> > +{
> > +	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
> > +	unsigned int mode, t;
> > +	unsigned int cd, fidi;
> > +	int ret = 0;
> > +
> > +	/* Disable RX and TX */
> > +	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RXDIS | ATMEL_US_TXDIS);
> > +	/* Disable interrupts */
> > +	atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
> > +
> > +	mode = atmel_uart_readl(port, ATMEL_US_MR);
> > +
> > +	if (iso7816conf->flags & SER_ISO7816_ENABLED) {
> > +		mode &= ~ATMEL_US_USMODE;
> > +
> > +		if ((iso7816conf->flags & SER_ISO7816_T_PARAM)
> > +					== SER_ISO7816_T(0)) {
> > +			mode |= ATMEL_US_USMODE_ISO7816_T0;
> > +			t = 0;
> > +		} else if ((iso7816conf->flags & SER_ISO7816_T_PARAM)
> > +					== SER_ISO7816_T(1)) {
> > +			mode |= ATMEL_US_USMODE_ISO7816_T1;
> > +			t = 1;
> > +		} else {
> > +			dev_warn(port->dev, "ISO7816 Type not supported. Resetting\n");
> > +			memset(iso7816conf, 0, sizeof(struct serial_iso7816));
> > +			goto err_out;
> > +		}
> > +
> > +		dev_dbg(port->dev, "Setting USART to ISO7816 mode T%d\n", t);
> > +
> > +		mode &= ~(ATMEL_US_USCLKS | ATMEL_US_CHRL
> > +			| ATMEL_US_NBSTOP | ATMEL_US_PAR);
> This could be merged in the mode &= line above.
> 

Ok

> > +
> > +		/* NACK configuration */
> > +		if ((iso7816conf->flags & SER_ISO7816_T_PARAM)
> > +					== SER_ISO7816_T(0))
> > +			mode |= ATMEL_US_DSNACK;
> > +		else
> > +			mode |= ATMEL_US_INACK;
> This could be also part of the if () above.
> 

Ok

> > +		/* select mck clock, and output  */
> > +		mode |= ATMEL_US_USCLKS_MCK | ATMEL_US_CLKO;
> > +		/* set parity for normal/inverse mode + max iterations */
> > +		mode |= ATMEL_US_PAR_EVEN | ATMEL_US_NBSTOP_1 | (3 << 24);
> Is this really needed ?
> In the documentation, I found:
> "The configuration is 8 data bits, even parity and 1 or 2 stop bits,
> regardless of the values programmed in the CHRL, MODE9, PAR and CHMODE
> fields."

It's not very clear. It is followed by "Parity Bit (PAR) can be used to
transmit in Normal or Inverse mode." and you have to choose 1 or 2 stop
bits.

> And, for MAX_ITERATIONS, could you add a macro instead of (x << 24) ?
> (ATMEL_US_MAX_ITER mask is already defined).

Yes

> And why 3 ? Should the user-space be allowed to control the max
> automatic iteration ? or is it more like a "same-value-for-every-one"
> thing ?
> 

It's an arbitrary choice. I have not seen any reference to number of
repetition in the ISO7816 spec but I may miss it. So I would say it's
not the same value for everyone. Is it useful to let the user setting
it? I don't know, maybe we can wait for a request to export this
setting.

> > +
> > +		cd = atmel_calc_cd(port, iso7816conf);
> > +		fidi = atmel_calc_fidi(port, iso7816conf);
> > +		if (fidi < 0) {
> I guess you meant (fidi == 0)
> Because fidi is unsigned and atmel_calc_fidi() returns also an unsigned.

Right.

> 
> > +			dev_warn(port->dev, "ISO7816 fidi = 0, Generator generates no signal\n");
> > +		} else if (fidi == 1 || fidi == 2) {
> > +			dev_err(port->dev, "ISO7816 fidi = %u, value not supported\n", fidi);
> > +			ret = -EINVAL;
> > +			goto err_out;
> > +		}
> And you may also want to check upper values ( <2048 or <65536, depending
> on the SoC)
> 

I'll do, I assumed that user space won't request weird values but it's
probably better to not trust him.

> > +
> > +		if (!(port->iso7816.flags & SER_ISO7816_ENABLED)) {
> > +			/* port not yet in iso7816 mode: store configuration */
> > +			atmel_port->backup_mode = atmel_uart_readl(port, ATMEL_US_MR);
> > +			atmel_port->backup_brgr = atmel_uart_readl(port, ATMEL_US_BRGR);
> > +		}
> > +
> > +		/* Actually set ISO7816 mode */
> > +		atmel_uart_writel(port, ATMEL_US_TTGR, iso7816conf->tg);
> iso7816conf->tg comes from user-space unchecked. AFAIK, max value is 255

Ok I'll check it.

> 
> > +		atmel_uart_writel(port, ATMEL_US_BRGR, cd);
> > +		atmel_uart_writel(port, ATMEL_US_FIDIR, fidi);
> > +
> > +		atmel_port->tx_done_mask = ATMEL_US_TXEMPTY | ATMEL_US_NACK | ATMEL_US_ITERATION;
> > +	} else {
> > +		dev_dbg(port->dev, "Setting UART to RS232\n");
> > +		/* back to last RS232 settings */
> > +		mode = atmel_port->backup_mode;
> > +		memset(iso7816conf, 0, sizeof(struct serial_iso7816));
> > +		atmel_uart_writel(port, ATMEL_US_TTGR, 0);
> > +		atmel_uart_writel(port, ATMEL_US_BRGR, atmel_port->backup_brgr);
> > +		atmel_uart_writel(port, ATMEL_US_FIDIR, 0x174);
> > +
> > +		if (atmel_use_pdc_tx(port))
> > +			atmel_port->tx_done_mask = ATMEL_US_ENDTX |
> > +						   ATMEL_US_TXBUFE;
> > +		else
> > +			atmel_port->tx_done_mask = ATMEL_US_TXRDY;
> > +	}
> > +
> > +	port->iso7816 = *iso7816conf;
> > +
> > +	atmel_uart_writel(port, ATMEL_US_MR, mode);
> > +
> > +err_out:
> > +	/* Enable interrupts */
> > +	atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);
> > +	/* Enable RX and TX */
> > +	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RXEN | ATMEL_US_TXEN);
> Is it all right to enable RX/TX unconditionally here ?
> 

As I didn't see any issue at the moment, I kept it like this. But I have
noticed this warning in the datasheet and I keep it in mind:
"Enabling both the receiver and the transmitter at the same time in
ISO7816 mode maylead to unpredictable results"

> > +
> > +	return ret;
> > +}
> > +
> >  /*
> >   * Return TIOCSER_TEMT when transmitter FIFO and Shift register is empty.
> >   */
> > @@ -481,8 +610,9 @@ static void atmel_stop_tx(struct uart_port *port)
> >  	/* Disable interrupts */
> >  	atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
> >  
> > -	if ((port->rs485.flags & SER_RS485_ENABLED) &&
> > -	    !(port->rs485.flags & SER_RS485_RX_DURING_TX))
> > +	if (((port->rs485.flags & SER_RS485_ENABLED) &&
> > +	     !(port->rs485.flags & SER_RS485_RX_DURING_TX)) ||
> > +	    port->iso7816.flags & SER_ISO7816_ENABLED)
> >  		atmel_start_rx(port);
> >  }
> >  
> > @@ -500,8 +630,9 @@ static void atmel_start_tx(struct uart_port *port)
> >  		return;
> >  
> >  	if (atmel_use_pdc_tx(port) || atmel_use_dma_tx(port))
> > -		if ((port->rs485.flags & SER_RS485_ENABLED) &&
> > -		    !(port->rs485.flags & SER_RS485_RX_DURING_TX))
> > +		if (((port->rs485.flags & SER_RS485_ENABLED) &&
> > +		     !(port->rs485.flags & SER_RS485_RX_DURING_TX)) ||
> > +		    port->iso7816.flags & SER_ISO7816_ENABLED)
> >  			atmel_stop_rx(port);
> >  
> >  	if (atmel_use_pdc_tx(port))
> > @@ -799,8 +930,9 @@ static void atmel_complete_tx_dma(void *arg)
> >  	 */
> >  	if (!uart_circ_empty(xmit))
> >  		atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx);
> > -	else if ((port->rs485.flags & SER_RS485_ENABLED) &&
> > -		 !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
> > +	else if (((port->rs485.flags & SER_RS485_ENABLED) &&
> > +		  !(port->rs485.flags & SER_RS485_RX_DURING_TX)) ||
> > +		 port->iso7816.flags & SER_ISO7816_ENABLED) {
> >  		/* DMA done, stop TX, start RX for RS485 */
> >  		atmel_start_rx(port);
> >  	}
> > @@ -1281,6 +1413,9 @@ atmel_handle_status(struct uart_port *port, unsigned int pending,
> >  			wake_up_interruptible(&port->state->port.delta_msr_wait);
> >  		}
> >  	}
> > +
> > +	if (pending & (ATMEL_US_NACK | ATMEL_US_ITERATION))
> > +		dev_dbg(port->dev, "ISO7816 ERROR (0x%08x)\n", pending);
> >  }
> >  
> >  /*
> > @@ -1373,8 +1508,9 @@ static void atmel_tx_pdc(struct uart_port *port)
> >  		atmel_uart_writel(port, ATMEL_US_IER,
> >  				  atmel_port->tx_done_mask);
> >  	} else {
> > -		if ((port->rs485.flags & SER_RS485_ENABLED) &&
> > -		    !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
> > +		if (((port->rs485.flags & SER_RS485_ENABLED) &&
> > +		     !(port->rs485.flags & SER_RS485_RX_DURING_TX)) ||
> > +		    port->iso7816.flags & SER_ISO7816_ENABLED) {
> >  			/* DMA done, stop TX, start RX for RS485 */
> >  			atmel_start_rx(port);
> >  		}
> > @@ -2099,6 +2235,17 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> >  		atmel_uart_writel(port, ATMEL_US_TTGR,
> >  				  port->rs485.delay_rts_after_send);
> >  		mode |= ATMEL_US_USMODE_RS485;
> > +	} else if (port->iso7816.flags & SER_ISO7816_ENABLED) {
> > +		atmel_uart_writel(port, ATMEL_US_TTGR, port->iso7816.tg);
> > +		/* select mck clock, and output  */
> > +		mode |= ATMEL_US_USCLKS_MCK | ATMEL_US_CLKO;
> > +		/* set max iterations */
> > +		mode |= (3 << 24);
> Same remark for macro / hardcoded value.
> 

OK

> > +		if ((port->iso7816.flags & SER_ISO7816_T_PARAM)
> > +				== SER_ISO7816_T(0))
> > +			mode |= ATMEL_US_USMODE_ISO7816_T0;
> > +		else
> > +			mode |= ATMEL_US_USMODE_ISO7816_T1;
> >  	} else if (termios->c_cflag & CRTSCTS) {
> >  		/* RS232 with hardware handshake (RTS/CTS) */
> >  		if (atmel_use_fifo(port) &&
> > @@ -2175,7 +2322,8 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> >  	}
> >  	quot = cd | fp << ATMEL_US_FP_OFFSET;
> >  
> > -	atmel_uart_writel(port, ATMEL_US_BRGR, quot);
> > +	if (!(port->iso7816.flags & SER_ISO7816_ENABLED))
> > +		atmel_uart_writel(port, ATMEL_US_BRGR, quot);
> >  	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
> >  	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
> >  	atmel_port->tx_stopped = false;
> > @@ -2355,6 +2503,7 @@ static int atmel_init_port(struct atmel_uart_port *atmel_port,
> >  	port->mapbase	= pdev->resource[0].start;
> >  	port->irq	= pdev->resource[1].start;
> >  	port->rs485_config	= atmel_config_rs485;
> > +	port->iso7816_config	= atmel_config_iso7816;
> >  	port->membase	= NULL;
> >  
> >  	memset(&atmel_port->rx_ring, 0, sizeof(atmel_port->rx_ring));
> > @@ -2379,7 +2528,8 @@ static int atmel_init_port(struct atmel_uart_port *atmel_port,
> >  	}
> >  
> >  	/* Use TXEMPTY for interrupt when rs485 else TXRDY or ENDTX|TXBUFE */
> > -	if (port->rs485.flags & SER_RS485_ENABLED)
> > +	if (port->rs485.flags & SER_RS485_ENABLED ||
> > +	    port->iso7816.flags & SER_ISO7816_ENABLED)
> please update the comment above.
> 

OK

> >  		atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
> >  	else if (atmel_use_pdc_tx(port)) {
> >  		port->fifosize = PDC_BUFFER_SIZE;
> > diff --git a/drivers/tty/serial/atmel_serial.h b/drivers/tty/serial/atmel_serial.h
> > index ba3a2437cde4..fff51f5fe8bc 100644
> > --- a/drivers/tty/serial/atmel_serial.h
> > +++ b/drivers/tty/serial/atmel_serial.h
> > @@ -124,7 +124,8 @@
> >  #define ATMEL_US_TTGR		0x28	/* Transmitter Timeguard Register */
> >  #define	ATMEL_US_TG		GENMASK(7, 0)	/* Timeguard Value */
> >  
> > -#define ATMEL_US_FIDI		0x40	/* FI DI Ratio Register */
> > +#define ATMEL_US_FIDIR		0x40	/* FI DI Ratio Register */
> > +#define ATMEL_US_FIDI		GENMASK(15, 0)	/* FIDI ratio */
> >  #define ATMEL_US_NER		0x44	/* Number of Errors Register */
> >  #define ATMEL_US_IF		0x4c	/* IrDA Filter Register */
> >  
> > 
> 
> Thanks !
> 
> Richard.

Thanks for your review, I'll send a new version.

Regards

Ludovic