Christophe Leroy [off-list ref] writes:

Le 14/12/2023 à 06:55, Nicholas Miehlbradt a écrit :

quoted

All elements of bounce_buffer are eventually read and passed to the
hypervisor so it should probably be fully initialized.

should or shall ?

quoted

Signed-off-by: Nicholas Miehlbradt <redacted>

Should be a Fixed: tag ?

quoted

---
  drivers/tty/hvc/hvc_vio.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/hvc/hvc_vio.c b/drivers/tty/hvc/hvc_vio.c
index 736b230f5ec0..1e88bfcdde20 100644
--- a/drivers/tty/hvc/hvc_vio.c
+++ b/drivers/tty/hvc/hvc_vio.c

@@ -227,7 +227,7 @@ static const struct hv_ops hvterm_hvsi_ops = {
  static void udbg_hvc_putc(char c)
  {
  	int count = -1;
-	unsigned char bounce_buffer[16];
+	unsigned char bounce_buffer[16] = { 0 };

Why 16 while we have a count of 1 in the call to hvterm_raw_put_chars() ?

Because hvterm_raw_put_chars() calls hvc_put_chars() which requires a 16
byte buffer, because it passes the buffer directly to firmware which
expects a 16 byte buffer.

It's a pretty horrible calling convention, but I guess it's to avoid
needing another bounce buffer inside hvc_put_chars().

We should probably do the change below, to at least document the
interface better.

cheers

diff --git a/arch/powerpc/include/asm/hvconsole.h b/arch/powerpc/include/asm/hvconsole.h
index ccb2034506f0..0ee7ed019e23 100644
--- a/arch/powerpc/include/asm/hvconsole.h
+++ b/arch/powerpc/include/asm/hvconsole.h

@@ -22,7 +22,7 @@
  * parm is included to conform to put_chars() function pointer template
  */
 extern int hvc_get_chars(uint32_t vtermno, char *buf, int count);
-extern int hvc_put_chars(uint32_t vtermno, const char *buf, int count);
+extern int hvc_put_chars(uint32_t vtermno, const char buf[16], int count);

 /* Provided by HVC VIO */
 void hvc_vio_init_early(void);

diff --git a/arch/powerpc/platforms/pseries/hvconsole.c b/arch/powerpc/platforms/pseries/hvconsole.c
index 1ac52963e08b..c40a82e49d59 100644
--- a/arch/powerpc/platforms/pseries/hvconsole.c
+++ b/arch/powerpc/platforms/pseries/hvconsole.c

@@ -52,7 +52,7 @@ EXPORT_SYMBOL(hvc_get_chars);
  *     firmware. Must be at least 16 bytes, even if count is less than 16.
  * @count: Send this number of characters.
  */
-int hvc_put_chars(uint32_t vtermno, const char *buf, int count)
+int hvc_put_chars(uint32_t vtermno, const char buf[16], int count)
 {
        unsigned long *lbuf = (unsigned long *) buf;
        long ret;

diff --git a/drivers/tty/hvc/hvc_vio.c b/drivers/tty/hvc/hvc_vio.c
index 736b230f5ec0..011b239a7e52 100644
--- a/drivers/tty/hvc/hvc_vio.c
+++ b/drivers/tty/hvc/hvc_vio.c

@@ -115,7 +115,7 @@ static int hvterm_raw_get_chars(uint32_t vtermno, char *buf, int count)
  *       you are sending fewer chars.
  * @count: number of chars to send.
  */
-static int hvterm_raw_put_chars(uint32_t vtermno, const char *buf, int count)
+static int hvterm_raw_put_chars(uint32_t vtermno, const char buf[16], int count)
 {
        struct hvterm_priv *pv = hvterm_privs[vtermno];