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From:   Nathan Lynch <nathanl@linux.ibm.com>
To:     linuxppc-dev@lists.ozlabs.org
Cc:     mpe@ellerman.id.au, linux-kernel@vger.kernel.org,
        gregkh@linuxfoundation.org, jirislaby@kernel.org
Subject: [PATCH] powerpc/udbg_hvc: retry putc on -EAGAIN
Date:   Fri, 14 May 2021 16:44:22 -0500
Message-Id: <20210514214422.3019105-1-nathanl@linux.ibm.com>
MIME-Version: 1.0
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hvterm_raw_put_chars() calls hvc_put_chars(), which may return -EAGAIN
when the underlying hcall returns a "busy" status, but udbg_hvc_putc()
doesn't handle this. When using xmon on a PowerVM guest, this can
result in incomplete or garbled output when printing relatively large
amounts of data quickly, such as when dumping the kernel log buffer.

Call again on -EAGAIN.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
---
 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 798f27f40cc2..76d2a7038095 100644
--- a/drivers/tty/hvc/hvc_vio.c
+++ b/drivers/tty/hvc/hvc_vio.c
@@ -249,7 +249,7 @@ static void udbg_hvc_putc(char c)
 			count = hvterm_hvsi_put_chars(0, &c, 1);
 			break;
 		}
-	} while(count == 0);
+	} while(count == 0 || count == -EAGAIN);
 }
 
 static int udbg_hvc_getc_poll(void)
-- 
2.30.2