[xen staging] console/serial: set the default transmit buffer size in Kconfig

[patchbot@xxxxxxx]

commit 4df2e99d731402da48afb19dc970ccab5a0814d6
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Jul 4 14:48:14 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 4 14:48:14 2022 +0200

    console/serial: set the default transmit buffer size in Kconfig
    
    Take the opportunity to convert the variable to read-only after init.
    
    No functional change intended.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/drivers/char/Kconfig  | 10 ++++++++++
 xen/drivers/char/serial.c |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/char/Kconfig b/xen/drivers/char/Kconfig
index e5f7b1d8eb..dec58bc993 100644
--- a/xen/drivers/char/Kconfig
+++ b/xen/drivers/char/Kconfig
@@ -74,3 +74,13 @@ config HAS_EHCI
        help
          This selects the USB based EHCI debug port to be used as a UART. If
          you have an x86 based system with USB, say Y.
+
+config SERIAL_TX_BUFSIZE
+       int "Size of the transmit serial buffer"
+       default 16384
+       help
+         Controls the default size of the transmit buffer (in bytes) used by
+         the serial driver.  Note the value provided will be rounded down to
+         the nearest power of 2.
+
+         Default value is 16384 (16kiB).
diff --git a/xen/drivers/char/serial.c b/xen/drivers/char/serial.c
index 5ecba0af33..f6c944bd30 100644
--- a/xen/drivers/char/serial.c
+++ b/xen/drivers/char/serial.c
@@ -16,7 +16,7 @@
 /* Never drop characters, even if the async transmit buffer fills. */
 /* #define SERIAL_NEVER_DROP_CHARS 1 */
 
-unsigned int __read_mostly serial_txbufsz = 16384;
+unsigned int __ro_after_init serial_txbufsz = CONFIG_SERIAL_TX_BUFSIZE;
 size_param("serial_tx_buffer", serial_txbufsz);
 
 #define mask_serial_rxbuf_idx(_i) ((_i)&(serial_rxbufsz-1))
--
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