[PATCH v3 15/24] xen/console: make console buffer size configurable

[Denis Mukhin via B4 Relay <devnull+dmukhin.ford.com@xxxxxxxxxx>]

From: Denis Mukhin <dmukhin@xxxxxxxx>

Add new CONRING_SIZE Kconfig parameter to specify the boot console buffer size
in bytes. The value is rounded to the nearest power of 2 to match existing
conring_size= behavior.

The supported range is [16KiB..128MiB].

Bump default size to 32 KiB.

Link: https://gitlab.com/xen-project/xen/-/issues/185
Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
 docs/misc/xen-command-line.pandoc |  7 +++++--
 xen/drivers/char/Kconfig          | 11 +++++++++++
 xen/drivers/char/console.c        |  9 ++++++---
 3 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index 
1a5ee3c91c5cc8bf653e5054211035b5d1bd560f..aeaee482f61aab41438a44eda470902e1e0806f8
 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -423,12 +423,15 @@ The following are examples of correct specifications:
     com1=baud=115200,parity=n,stop-bits=1,io-base=0x3f8,reg-width=4
 
 ### conring_size
-> `= <size>`
+> `= <size-in-bytes>`
 
-> Default: `conring_size=16k`
+> Default: `conring_size=32k`
 
 Specify the size of the console ring buffer.
 
+The console ring buffer size can be selected at build time via
+CONFIG_CONRING_SIZE.
+
 ### console
 > `= List of [ vga | com1[H,L] | com2[H,L] | pv | dbgp | ehci | xhci | none ]`
 
diff --git a/xen/drivers/char/Kconfig b/xen/drivers/char/Kconfig
index 
e6e12bb4139717f9319031f51f5d20155d2caee2..f7e193e29e2d9ac7c1b878e13f3fb1ce444f31b5
 100644
--- a/xen/drivers/char/Kconfig
+++ b/xen/drivers/char/Kconfig
@@ -96,6 +96,17 @@ config SERIAL_TX_BUFSIZE
 
          Default value is 32768 (32KiB).
 
+config CONRING_SIZE
+       int "Console buffer size"
+       default 32768
+       help
+         Select the boot console buffer size (in bytes).
+         Note, the value provided will be rounded down to the nearest power of 
2.
+         Run-time console buffer size is the same as the boot console size,
+         unless enforced via 'conring_size=' boot parameter.
+
+         Default value is 32768 (32KiB). The supported range is 
[16KiB..128MiB].
+
 config XHCI
        bool "XHCI DbC UART driver"
        depends on X86
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 
1308236403df8a0f87aeb7e2c00a036c2d8433a7..a33132b8fad95a1ad7e0aab4aef3fa3e46a5c03a
 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -100,12 +100,15 @@ static int cf_check parse_console_timestamps(const char 
*s);
 custom_runtime_param("console_timestamps", parse_console_timestamps,
                      con_timestamp_mode_upd);
 
-/* conring_size: allows a large console ring than default (16kB). */
+/* conring_size: allows a large console ring than default (32 KiB). */
 static uint32_t __initdata opt_conring_size;
 size_param("conring_size", opt_conring_size);
 
-#define _CONRING_SIZE 16384
-#define CONRING_IDX_MASK(i) ((i)&(conring_size-1))
+#define _CONRING_SIZE       (1UL << (31 - __builtin_clz(CONFIG_CONRING_SIZE)))
+_Static_assert(_CONRING_SIZE >= 4096 && _CONRING_SIZE <= MB(128),
+    "CONFIG_CONRING_SIZE must be in [4K..128M] range");
+
+#define CONRING_IDX_MASK(i) ( (i) & (conring_size - 1) )
 static char __initdata _conring[_CONRING_SIZE];
 static char *__read_mostly conring = _conring;
 static uint32_t __read_mostly conring_size = _CONRING_SIZE;

-- 
2.34.1