OMAP3xxx and OMAP4430 UART IP blocks have a restriction wrt RX FIFO. Empty RX fifo read causes an abort. OMAP3xxx: UART IP revision >= 0x52 have this issue MVR register format is: Bits Field Name Description Type Reset 31:8 RESERVED RO 0x0 7:4 MAJOR Major revision number of the module. RO 0x-- 3:0 MINOR Minor revision number of the module. RO 0x-- OMAP4xxx: All revisions have this issue Revision id check is not used as the format of MVR resigster has changed For omap4 MVR register reads as: 0x50410602 => Revision id = 0x0602 Format of MVR register on omap4 is: (Courtesy: Cousson, Benoit) Bits Field Name Description Type Reset 31:30 SCHEME Scheme revision number of module RO 0x1 29:28 RESERVED RO 0x1 27:16 FUNC Function revision number of module RO 0x041 15:11 RTL Rtl revision number of module RO 0x00 10:8 MAJOR Major revision number of the module. RO 0x6 7:6 CUSTOM Custom revision number of the module. RO 0x0 5:0 MINOR Minor revision number of the module. RO 0x02 Override the default 8250 read handler: mem_serial_in() by a custom handler: serial_in_8250() which makes sure that RX fifo is not read when empty tested on zoom3(3630) board Cc: Cousson, Benoit <b-cousson@xxxxxx> Signed-off-by: Vikram Pandita <vikram.pandita@xxxxxx> --- History of Patch: V1: http://patchwork.kernel.org/patch/61671/ http://patchwork.kernel.org/patch/61672/ V2: Incorporate approach suggested by Tony L Introduce IP version check in mach-omap2/serial.c file V3: Change #ifdef OMAP4 to cpu_is_omap44xx() diff --git a/arch/arm/mach-omap2/serial.c b/arch/arm/mach-omap2/serial.c index 2e17b57..e853115 100644 --- a/arch/arm/mach-omap2/serial.c +++ b/arch/arm/mach-omap2/serial.c @@ -33,6 +33,7 @@ #include "pm.h" #include "prm-regbits-34xx.h" +#define UART_OMAP_NO_EMPTY_FIFO_READ_IP_REV 0x52 #define UART_OMAP_WER 0x17 /* Wake-up enable register */ #define DEFAULT_TIMEOUT (5 * HZ) @@ -572,6 +573,23 @@ static struct omap_uart_state omap_uart[] = { #endif }; +/* + * Override the default 8250 read handler: mem_serial_in() + * Empty RX fifo read causes an abort on omap3630 and omap4 + * This function makes sure that an empty rx fifo is not read on these silicons + * (OMAP1/2/3430 are not affected) + */ +static unsigned int serial_in_override(struct uart_port *up, int offset) +{ + if (UART_RX == offset) { + unsigned int lsr; + lsr = serial_read_reg(omap_uart[up->line].p, UART_LSR); + if (!(lsr & UART_LSR_DR)) + return -EPERM; + } + return serial_read_reg(omap_uart[up->line].p, offset); +} + void __init omap_serial_early_init(void) { int i; @@ -650,5 +668,15 @@ void __init omap_serial_init(void) device_init_wakeup(dev, true); DEV_CREATE_FILE(dev, &dev_attr_sleep_timeout); } + + /* omap44xx: Never read empty UART fifo + * omap3xxx: Never read empty UART fifo on UARTs + * with IP rev >=0x52 + */ + if (cpu_is_omap44xx()) + uart->p->serial_in = serial_in_override; + else if ((serial_read_reg(uart->p, UART_OMAP_MVER) & 0xFF) + >= UART_OMAP_NO_EMPTY_FIFO_READ_IP_REV) + uart->p->serial_in = serial_in_override; } } -- 1.6.6.rc0.66.ge160d -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
