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SubjectRe: serial: 8250 fails to detect Exar XR16L2551 correctly
On Tue, Jul 05, 2005 at 03:19:40PM +0100, David Vrabel wrote:
> The 8250 serial driver detects the Exar XR16L2551 as a 16550A. The
> XR16L2551 has an EFR register and sleep capabilities (UART_CAP_FIFO |
> UART_CAP_EFR | UART_CAP_SLEEP). However, broken_efr() thinks it's a
> buggy Exar ST16C255x.

Grumble!

> Any suggestion on how to differentiate between the two parts? Exar have
> made the ST16C255x with the same registers as the XR16L255x...

If they're 100% identical in terms of the registers, then it's probably
impossible to differentiate between the two.

> Perhaps it's okay for the ST16C255x to be detected as something with
> UART_CAP_EFR | UART_CAP_SLEEP even if it doesn't work? i.e., by removing
> broken_efr().

I don't know - maybe Alex Williamson can try your patch out.

> Also, the initial IER test was failing (after a soft reboot) with the
> XR16L2551 part since the sleep mode bit was set but was read-only. It
> seems sensible to make this test only look at the lower 4 bits.

... or maybe this can be used to test for the buggy version.

> Index: linux-2.6-working/drivers/serial/8250.c
> ===================================================================
> --- linux-2.6-working.orig/drivers/serial/8250.c 2005-07-04 13:43:13.000000000 +0100
> +++ linux-2.6-working/drivers/serial/8250.c 2005-07-05 15:08:05.000000000 +0100
> @@ -249,6 +249,14 @@
> .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10,
> .flags = UART_CAP_FIFO | UART_CAP_UUE,
> },
> + [PORT_XR16550] = {
> + .name = "XR16550",
> + .fifo_size = 16,
> + .tx_loadsz = 16,
> + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01 |
> + UART_FCR_T_TRIG_00,

The docs I've just pulled of Exar's site imply that the XR16L2551
doesn't have a transmit trigger threshold, so UART_FCR_T_TRIG_00
shouldn't be specified here. Also, is there a reason for restricting
the RX trigger level to 4 instead of 8 bytes?

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
%state
pending
%patch
Index: linux-2.6-working/drivers/serial/8250.c
===================================================================
--- linux-2.6-working.orig/drivers/serial/8250.c 2005-07-04 13:43:13.000000000 +0100
+++ linux-2.6-working/drivers/serial/8250.c 2005-07-05 15:08:05.000000000 +0100
@@ -249,6 +249,14 @@
.fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10,
.flags = UART_CAP_FIFO | UART_CAP_UUE,
},
+ [PORT_XR16550] = {
+ .name = "XR16550",
+ .fifo_size = 16,
+ .tx_loadsz = 16,
+ .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01 |
+ UART_FCR_T_TRIG_00,
+ .flags = UART_CAP_FIFO | UART_CAP_EFR | UART_CAP_SLEEP,
+ },
};

static _INLINE_ unsigned int serial_in(struct uart_8250_port *up, int offset)
@@ -573,6 +581,15 @@
up->port.type = PORT_16850;
return;
}
+ /* The Exar XR16L255x has an DVID of 0x02. This will misdetect the
+ * Exar ST16C255x (A2 revision) which has registers like the XR16L255x
+ * but doesn't have a working sleep mode. However, it's safe to claim
+ * sleep capabilities even if they don't work. See also
+ * http://www.exar.com/info.php?pdf=dan180_oct2004.pdf */
+ if (id2 == 0x02) {
+ up->port.type = PORT_XR16550;
+ return;
+ }

/*
* It wasn't an XR16C850.
@@ -585,7 +602,7 @@
*/
if (size_fifo(up) == 64)
up->port.type = PORT_16654;
- else
+ else if(size_fifo(up) == 32)
up->port.type = PORT_16650V2;
}

@@ -611,19 +628,6 @@
up->port.type = PORT_16450;
}

-static int broken_efr(struct uart_8250_port *up)
-{
- /*
- * Exar ST16C2550 "A2" devices incorrectly detect as
- * having an EFR, and report an ID of 0x0201. See
- * http://www.exar.com/info.php?pdf=dan180_oct2004.pdf
- */
- if (autoconfig_read_divisor_id(up) == 0x0201 && size_fifo(up) == 16)
- return 1;
-
- return 0;
-}
-
/*
* We know that the chip has FIFOs. Does it have an EFR? The
* EFR is located in the same register position as the IIR and
@@ -661,7 +665,7 @@
* (other ST16C650V2 UARTs, TI16C752A, etc)
*/
serial_outp(up, UART_LCR, 0xBF);
- if (serial_in(up, UART_EFR) == 0 && !broken_efr(up)) {
+ if (serial_in(up, UART_EFR) == 0) {
DEBUG_AUTOCONF("EFRv2 ");
autoconfig_has_efr(up);
return;
@@ -828,7 +832,7 @@
#endif
scratch3 = serial_inp(up, UART_IER);
serial_outp(up, UART_IER, scratch);
- if (scratch2 != 0 || scratch3 != 0x0F) {
+ if ((scratch2 & 0x0f) != 0 || (scratch3 & 0x0f) != 0x0F) {
/*
* We failed; there's nothing here
*/
Index: linux-2.6-working/include/linux/serial_core.h
===================================================================
--- linux-2.6-working.orig/include/linux/serial_core.h 2005-07-04 13:43:13.000000000 +0100
+++ linux-2.6-working/include/linux/serial_core.h 2005-07-05 15:07:58.000000000 +0100
@@ -39,7 +39,8 @@
#define PORT_RSA 13
#define PORT_NS16550A 14
#define PORT_XSCALE 15
-#define PORT_MAX_8250 15 /* max port ID */
+#define PORT_XR16550 16
+#define PORT_MAX_8250 16 /* max port ID */

/*
* ARM specific type numbers. These are not currently guaranteed
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