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Date: Tue, 01 May 2018 19:48:58 +1000
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: Nicholas Piggin <npiggin@...il.com>, linuxppc-dev@...ts.ozlabs.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/15] powerpc/powernv: implement opal_put_chars_atomic
On Tue, 2018-05-01 at 00:55 +1000, Nicholas Piggin wrote:
> The RAW console does not need writes to be atomic, so relax
> opal_put_chars to be able to do partial writes, and implement an
> _atomic variant which does not take a spinlock. This API is used
> in xmon, so the less locking that is used, the better chance there
> is that a crash can be debugged.
Same comment I already had :-) "atomic" in Linux tends to mean
something else (ie, atomic context), so I'd rather have something
like opal_put_chars_sync() or such...
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> ---
> arch/powerpc/include/asm/opal.h | 1 +
> arch/powerpc/platforms/powernv/opal.c | 37 +++++++++++++++++++--------
> drivers/tty/hvc/hvc_opal.c | 18 +++++++++----
> 3 files changed, 41 insertions(+), 15 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
> index bbff49fab0e5..5d7072411561 100644
> --- a/arch/powerpc/include/asm/opal.h
> +++ b/arch/powerpc/include/asm/opal.h
> @@ -303,6 +303,7 @@ extern void opal_configure_cores(void);
>
> extern int opal_get_chars(uint32_t vtermno, char *buf, int count);
> extern int opal_put_chars(uint32_t vtermno, const char *buf, int total_len);
> +extern int opal_put_chars_atomic(uint32_t vtermno, const char *buf, int total_len);
> extern int opal_flush_console(uint32_t vtermno);
>
> extern void hvc_opal_init_early(void);
> diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
> index 55d4b1983110..bcdb90ada938 100644
> --- a/arch/powerpc/platforms/powernv/opal.c
> +++ b/arch/powerpc/platforms/powernv/opal.c
> @@ -344,9 +344,9 @@ int opal_get_chars(uint32_t vtermno, char *buf, int count)
> return 0;
> }
>
> -int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
> +static int __opal_put_chars(uint32_t vtermno, const char *data, int total_len, bool atomic)
> {
> - unsigned long flags;
> + unsigned long flags = 0 /* shut up gcc */;
> int written;
> __be64 olen;
> s64 rc;
> @@ -354,11 +354,8 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
> if (!opal.entry)
> return -ENODEV;
>
> - /* We want put_chars to be atomic to avoid mangling of hvsi
> - * packets. To do that, we first test for room and return
> - * -EAGAIN if there isn't enough.
> - */
> - spin_lock_irqsave(&opal_write_lock, flags);
> + if (atomic)
> + spin_lock_irqsave(&opal_write_lock, flags);
> rc = opal_console_write_buffer_space(vtermno, &olen);
> if (rc || be64_to_cpu(olen) < total_len) {
> /* Closed -> drop characters */
> @@ -391,14 +388,18 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
>
> written = be64_to_cpu(olen);
> if (written < total_len) {
> - /* Should not happen */
> - pr_warn("atomic console write returned partial len=%d written=%d\n", total_len, written);
> + if (atomic) {
> + /* Should not happen */
> + pr_warn("atomic console write returned partial "
> + "len=%d written=%d\n", total_len, written);
> + }
> if (!written)
> written = -EAGAIN;
> }
>
> out:
> - spin_unlock_irqrestore(&opal_write_lock, flags);
> + if (atomic)
> + spin_unlock_irqrestore(&opal_write_lock, flags);
>
> /* In the -EAGAIN case, callers loop, so we have to flush the console
> * here in case they have interrupts off (and we don't want to wait
> @@ -412,6 +413,22 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
> return written;
> }
>
> +int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
> +{
> + return __opal_put_chars(vtermno, data, total_len, false);
> +}
> +
> +/*
> + * opal_put_chars_atomic will not perform partial-writes. Data will be
> + * atomically written to the terminal or not at all. This is not strictly
> + * true at the moment because console space can race with OPAL's console
> + * writes.
> + */
> +int opal_put_chars_atomic(uint32_t vtermno, const char *data, int total_len)
> +{
> + return __opal_put_chars(vtermno, data, total_len, true);
> +}
> +
> int opal_flush_console(uint32_t vtermno)
> {
> s64 rc;
> diff --git a/drivers/tty/hvc/hvc_opal.c b/drivers/tty/hvc/hvc_opal.c
> index af122ad7f06d..0a72f98ee082 100644
> --- a/drivers/tty/hvc/hvc_opal.c
> +++ b/drivers/tty/hvc/hvc_opal.c
> @@ -183,9 +183,15 @@ static int hvc_opal_probe(struct platform_device *dev)
> return -ENOMEM;
> pv->proto = proto;
> hvc_opal_privs[termno] = pv;
> - if (proto == HV_PROTOCOL_HVSI)
> - hvsilib_init(&pv->hvsi, opal_get_chars, opal_put_chars,
> + if (proto == HV_PROTOCOL_HVSI) {
> + /*
> + * We want put_chars to be atomic to avoid mangling of
> + * hvsi packets.
> + */
> + hvsilib_init(&pv->hvsi,
> + opal_get_chars, opal_put_chars_atomic,
> termno, 0);
> + }
>
> /* Instanciate now to establish a mapping index==vtermno */
> hvc_instantiate(termno, termno, ops);
> @@ -376,8 +382,9 @@ void __init hvc_opal_init_early(void)
> else if (of_device_is_compatible(stdout_node,"ibm,opal-console-hvsi")) {
> hvc_opal_boot_priv.proto = HV_PROTOCOL_HVSI;
> ops = &hvc_opal_hvsi_ops;
> - hvsilib_init(&hvc_opal_boot_priv.hvsi, opal_get_chars,
> - opal_put_chars, index, 1);
> + hvsilib_init(&hvc_opal_boot_priv.hvsi,
> + opal_get_chars, opal_put_chars_atomic,
> + index, 1);
> /* HVSI, perform the handshake now */
> hvsilib_establish(&hvc_opal_boot_priv.hvsi);
> pr_devel("hvc_opal: Found HVSI console\n");
> @@ -409,7 +416,8 @@ void __init udbg_init_debug_opal_hvsi(void)
> hvc_opal_privs[index] = &hvc_opal_boot_priv;
> hvc_opal_boot_termno = index;
> udbg_init_opal_common();
> - hvsilib_init(&hvc_opal_boot_priv.hvsi, opal_get_chars, opal_put_chars,
> + hvsilib_init(&hvc_opal_boot_priv.hvsi,
> + opal_get_chars, opal_put_chars_atomic,
> index, 1);
> hvsilib_establish(&hvc_opal_boot_priv.hvsi);
> }
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