[PATCH 1/2] ns16550: do not override fifo size if explicitly set - Marek Marczykowski-Górecki

From: "Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>
To: xen-devel@lists.xenproject.org
Cc: "Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Ian Jackson" <iwj@xenproject.org>,
	"Jan Beulich" <jbeulich@suse.com>,
	"Julien Grall" <julien@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>
Subject: [PATCH 1/2] ns16550: do not override fifo size if explicitly set
Date: Fri, 13 Aug 2021 20:31:38 +0200	[thread overview]
Message-ID: <20210813183139.391546-1-marmarek@invisiblethingslab.com> (raw)

If fifo size is already set via uart_params, do not force it to 16 - which
may not match the actual hardware. Specifically Exar cards have fifo of
256 bytes.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
 xen/drivers/char/ns16550.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 16a73d0c0e47..97b85b0225cc 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -357,7 +357,8 @@ static void __init ns16550_init_preirq(struct serial_port *port)
     ns16550_setup_preirq(uart);
 
     /* Check this really is a 16550+. Otherwise we have no FIFOs. */
-    if ( ((ns_read_reg(uart, UART_IIR) & 0xc0) == 0xc0) &&
+    if ( uart->fifo_size <= 1 &&
+         ((ns_read_reg(uart, UART_IIR) & 0xc0) == 0xc0) &&
          ((ns_read_reg(uart, UART_FCR) & UART_FCR_TRG14) == UART_FCR_TRG14) )
         uart->fifo_size = 16;
 }
-- 
2.31.1


