Messages in this thread Patch in this message | | | From | Cristian Marussi <> | Subject | [RFC PATCH 04/10] firmware: arm_scmi: Add support for atomic transports | Date | Sun, 6 Jun 2021 23:12:26 +0100 |
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An SCMI transport can declare itself as .atomic_capable in order to signal to the SCMI core that all its transmit path can be executed in atomic context: the core as a consequence will take care not to sleep to in the corresponding rx path while waiting for a response or a delayed response.
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com> --- --- drivers/firmware/arm_scmi/common.h | 1 + drivers/firmware/arm_scmi/driver.c | 144 +++++++++++++++++++++++------ 2 files changed, 119 insertions(+), 26 deletions(-)
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h index 8f4e6ebfc0ef..42cf1c79c096 100644 --- a/drivers/firmware/arm_scmi/common.h +++ b/drivers/firmware/arm_scmi/common.h @@ -333,6 +333,7 @@ struct scmi_device *scmi_child_dev_find(struct device *parent, * mechanism instead of completion interrupts even if available. */ struct scmi_desc { + bool atomic_capable; const struct scmi_transport_ops *ops; int max_rx_timeout_ms; int max_msg; diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c index c11ff49f6b62..276b729f2f43 100644 --- a/drivers/firmware/arm_scmi/driver.c +++ b/drivers/firmware/arm_scmi/driver.c @@ -360,6 +360,10 @@ static void scmi_handle_response(struct scmi_chan_info *cinfo, info->desc->ops->clear_channel(cinfo); complete(xfer->async_done); } else { + /* + * This same xfer->done completion is used in atomic mode as a + * flag for polling. + */ complete(&xfer->done); } } @@ -410,8 +414,6 @@ static void xfer_put(const struct scmi_protocol_handle *ph, __scmi_xfer_put(&info->tx_minfo, xfer); } -#define SCMI_MAX_POLL_TO_NS (100 * NSEC_PER_USEC) - static bool scmi_xfer_done_no_timeout(struct scmi_chan_info *cinfo, struct scmi_xfer *xfer, ktime_t stop) { @@ -421,6 +423,79 @@ static bool scmi_xfer_done_no_timeout(struct scmi_chan_info *cinfo, ktime_after(ktime_get(), stop); } +static bool xfer_complete_or_timeout(struct completion *done, ktime_t stop) +{ + return try_wait_for_completion(done) || ktime_after(ktime_get(), stop); +} + +static int spin_for_completion_timeout(struct completion *done, int timeout_ms) +{ + ktime_t stop = ktime_add_ms(ktime_get(), timeout_ms); + + spin_until_cond(xfer_complete_or_timeout(done, stop)); + if (ktime_after(ktime_get(), stop)) + return -ETIMEDOUT; + + return 0; +} + +/** + * scmi_wait_for_message_response - An helper to group all the possible ways of + * waiting for a synchronous message response. + * + * @cinfo: SCMI channel info + * @xfer: Reference to the transfer being waited for. + * + * Chooses waiting strategy (sleep-waiting vs busy-waiting) depending on flags + * configuration like xfer->hdr.poll_completion and scmi_desc.atomic.capable. + * + * Return: 0 on Success, error otherwise. + */ +static int scmi_wait_for_message_response(struct scmi_chan_info *cinfo, + struct scmi_xfer *xfer) +{ + struct scmi_info *info = handle_to_scmi_info(cinfo->handle); + struct device *dev = info->dev; + int ret = 0, timeout_ms = info->desc->max_rx_timeout_ms; + + if (!xfer->hdr.poll_completion) { + if (!info->desc->atomic_capable) { + if (!wait_for_completion_timeout(&xfer->done, + msecs_to_jiffies(timeout_ms))) { + dev_err(dev, "timed out in resp(caller: %pS)\n", + (void *)_RET_IP_); + ret = -ETIMEDOUT; + } + } else { + /* Poll on xfer->done waiting for completion by interrupt */ + ret = spin_for_completion_timeout(&xfer->done, + timeout_ms); + if (ret) + dev_err(dev, + "timed out in resp(caller: %pS) - atomic\n", + (void *)_RET_IP_); + } + } else { + /* + * Poll on xfer using transport provided .poll_done(); + * assumes no completion interrupt was available. + */ + ktime_t stop = ktime_add_ms(ktime_get(), timeout_ms); + + spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer, stop)); + if (ktime_after(ktime_get(), stop)) { + dev_err(dev, + "timed out in resp(caller: %pS) - polling\n", + (void *)_RET_IP_); + ret = -ETIMEDOUT; + } else { + info->desc->ops->fetch_response(cinfo, xfer); + } + } + + return ret; +} + /** * do_xfer() - Do one transfer * @@ -435,7 +510,6 @@ static int do_xfer(const struct scmi_protocol_handle *ph, struct scmi_xfer *xfer) { int ret; - int timeout; const struct scmi_protocol_instance *pi = ph_to_pi(ph); struct scmi_info *info = handle_to_scmi_info(pi->handle); struct device *dev = info->dev; @@ -467,25 +541,7 @@ static int do_xfer(const struct scmi_protocol_handle *ph, return ret; } - if (xfer->hdr.poll_completion) { - ktime_t stop = ktime_add_ns(ktime_get(), SCMI_MAX_POLL_TO_NS); - - spin_until_cond(scmi_xfer_done_no_timeout(cinfo, xfer, stop)); - - if (ktime_before(ktime_get(), stop)) - info->desc->ops->fetch_response(cinfo, xfer); - else - ret = -ETIMEDOUT; - } else { - /* And we wait for the response. */ - timeout = msecs_to_jiffies(info->desc->max_rx_timeout_ms); - if (!wait_for_completion_timeout(&xfer->done, timeout)) { - dev_err(dev, "timed out in resp(caller: %pS)\n", - (void *)_RET_IP_); - ret = -ETIMEDOUT; - } - } - + ret = scmi_wait_for_message_response(cinfo, xfer); if (!ret && xfer->hdr.status) ret = scmi_to_linux_errno(xfer->hdr.status); @@ -507,7 +563,7 @@ static void reset_rx_to_maxsz(const struct scmi_protocol_handle *ph, xfer->rx.len = info->desc->max_msg_size; } -#define SCMI_MAX_RESPONSE_TIMEOUT (2 * MSEC_PER_SEC) +#define SCMI_DRESP_TIMEOUT (2 * MSEC_PER_SEC) /** * do_xfer_with_response() - Do one transfer and wait until the delayed @@ -516,14 +572,33 @@ static void reset_rx_to_maxsz(const struct scmi_protocol_handle *ph, * @ph: Pointer to SCMI protocol handle * @xfer: Transfer to initiate and wait for response * + * Avois sleeping in favour of busy-waiting if the underlying transport was + * declared as .atomic_capable. + * + * Note that using asynchronous commands when running on top of atomic + * transports should be avoided since it could cause long busy-waiting here, + * but, once a transport is declared atomic, upper layers using the SCMI stack + * can freely make assumptions about the 'non-sleeping' nature of the stack + * (e.g. Clock framework) and it cannot be excluded that asynchronous commands + * could be exposed by the platform and so used. + * + * The only other option would have been to refrain from using any asynchronous + * command even if made available, when an atomic transport is detected, and + * instead forcibly use the synchronous version (thing that can be easily + * attained at the protocol layer), but this would also have led to longer + * stalls of the channel for synchronous commands and possibly timeouts. + * (in other words there is usually a good reason if a platform provides an + * asynchronous version of a command and we should prefer to use it) + * * Return: -ETIMEDOUT in case of no delayed response, if transmit error, * return corresponding error, else if all goes well, return 0. */ static int do_xfer_with_response(const struct scmi_protocol_handle *ph, struct scmi_xfer *xfer) { - int ret, timeout = msecs_to_jiffies(SCMI_MAX_RESPONSE_TIMEOUT); + int ret, timeout = msecs_to_jiffies(SCMI_DRESP_TIMEOUT); const struct scmi_protocol_instance *pi = ph_to_pi(ph); + struct scmi_info *info = handle_to_scmi_info(pi->handle); DECLARE_COMPLETION_ONSTACK(async_response); xfer->hdr.protocol_id = pi->proto->id; @@ -531,8 +606,25 @@ static int do_xfer_with_response(const struct scmi_protocol_handle *ph, xfer->async_done = &async_response; ret = do_xfer(ph, xfer); - if (!ret && !wait_for_completion_timeout(xfer->async_done, timeout)) - ret = -ETIMEDOUT; + if (!ret) { + if (!info->desc->atomic_capable) { + if (!wait_for_completion_timeout(xfer->async_done, + timeout)) { + dev_err(ph->dev, + "timed out in delayed resp(caller: %pS)\n", + (void *)_RET_IP_); + ret = -ETIMEDOUT; + } + } else { + ret = spin_for_completion_timeout(xfer->async_done, + SCMI_DRESP_TIMEOUT); + } + + if (ret) + dev_err(ph->dev, + "timed out in delayed resp(caller: %pS) - atomic\n", + (void *)_RET_IP_); + } xfer->async_done = NULL; return ret; -- 2.17.1
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