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+.. _skiboot-5.4.8:
+
+=============
+skiboot-5.4.8
+=============
+
+skiboot-5.4.8 was released on Wednesday October 11th, 2017. It replaces
+:ref:`skiboot-5.4.7` as the current stable release in the 5.4.x series.
+
+Over :ref:`skiboot-5.4.7`, we have a few bug fixes for FSP platforms:
+
+- libflash/file: Handle short read()s and write()s correctly
+
+  Currently we don't move the buffer along for a short read() or write()
+  and nor do we request only the remaining amount.
+- FSP/NVRAM: Handle "get vNVRAM statistics" command
+
+  FSP sends MBOX command (cmd : 0xEB, subcmd : 0x05, mod : 0x00) to get vNVRAM
+  statistics. OPAL doesn't maintain any such statistics. Hence return
+  FSP_STATUS_INVALID_SUBCMD.
+
+    Sample OPAL log: ::
+
+      [16944.384670488,3] FSP: Unhandled message eb0500
+      [16944.474110465,3] FSP: Unhandled message eb0500
+      [16945.111280784,3] FSP: Unhandled message eb0500
+      [16945.293393485,3] FSP: Unhandled message eb0500
+- FSP/CONSOLE: Limit number of error logging
+
+  Commit c8a7535f (FSP/CONSOLE: Workaround for unresponsive ipmi daemon, added
+  in skiboot 5.4.6 and 5.7-rc1) added error logging when buffer is full. In some
+  corner cases kernel may call this function multiple time and we may endup logging
+  error again and again.
+
+  This patch fixes it by generating error log only once.
+
+- FSP/CONSOLE: Fix fsp_console_write_buffer_space() call
+
+  Kernel calls fsp_console_write_buffer_space() to check console buffer space
+  availability. If there is enough buffer space to write data, then kernel will
+  call fsp_console_write() to write actual data.
+
+  In some extreme corner cases (like one explained in commit c8a7535f)
+  console becomes full and this function returns 0 to kernel (or space available
+  in console buffer < next incoming data size). Kernel will continue retrying
+  until it gets enough space. So we will start seeing RCU stalls.
+
+  This patch keeps track of previous available space. If previous space is same
+  as current means not enough space in console buffer to write incoming data.
+  It may be due to very high console write operation and slow response from FSP
+  -OR- FSP has stopped processing data (ex: because of ipmi daemon died). At this
+  point we will start timer with timeout of SER_BUFFER_OUT_TIMEOUT (10 secs).
+  If situation is not improved within 10 seconds means something went bad. Lets
+  return OPAL_RESOURCE so that kernel can drop console write and continue.
+- FSP/CONSOLE: Close SOL session during R/R
+
+  Presently we are not closing SOL and FW console sessions during R/R. Host will
+  continue to write to SOL buffer during FSP R/R. If there is heavy console write
+  operation happening during FSP R/R (like running `top` command inside console),
+  then at some point console buffer becomes full. fsp_console_write_buffer_space()
+  returns 0 (or less than required space to write data) to host. While one thread
+  is busy writing to console, if some other threads tries to write data to console
+  we may see RCU stalls (like below) in kernel.
+
+  kernel call trace: ::
+
+    [ 2082.828363] INFO: rcu_sched detected stalls on CPUs/tasks: { 32} (detected by 16, t=6002 jiffies, g=23154, c=23153, q=254769)
+    [ 2082.828365] Task dump for CPU 32:
+    [ 2082.828368] kworker/32:3    R  running task        0  4637      2 0x00000884
+    [ 2082.828375] Workqueue: events dump_work_fn
+    [ 2082.828376] Call Trace:
+    [ 2082.828382] [c000000f1633fa00] [c00000000013b6b0] console_unlock+0x570/0x600 (unreliable)
+    [ 2082.828384] [c000000f1633fae0] [c00000000013ba34] vprintk_emit+0x2f4/0x5c0
+    [ 2082.828389] [c000000f1633fb60] [c00000000099e644] printk+0x84/0x98
+    [ 2082.828391] [c000000f1633fb90] [c0000000000851a8] dump_work_fn+0x238/0x250
+    [ 2082.828394] [c000000f1633fc60] [c0000000000ecb98] process_one_work+0x198/0x4b0
+    [ 2082.828396] [c000000f1633fcf0] [c0000000000ed3dc] worker_thread+0x18c/0x5a0
+    [ 2082.828399] [c000000f1633fd80] [c0000000000f4650] kthread+0x110/0x130
+    [ 2082.828403] [c000000f1633fe30] [c000000000009674] ret_from_kernel_thread+0x5c/0x68
+
+  Hence lets close SOL (and FW console) during FSP R/R.
+
+- FSP/CONSOLE: Do not associate unavailable console
+
+  Presently OPAL sends associate/unassociate MBOX command for all
+  FSP serial console (like below OPAL message). We have to check
+  console is available or not before sending this message.
+
+  OPAL log: ::
+
+    [ 5013.227994012,7] FSP: Reassociating HVSI console 1
+    [ 5013.227997540,7] FSP: Reassociating HVSI console 2
+- FSP: Disable PSI link whenever FSP tells OPAL about impending Reset/Reload
+
+  Commit 42d5d047 fixed scenario where DPO has been initiated, but FSP went
+  into reset before the CEC power down came in. But this is generic issue
+  that can happen in normal shutdown path as well.
+
+  Hence disable PSI link as soon as we detect FSP impending R/R.
+
+
+- fsp: return OPAL_BUSY_EVENT on failure sending FSP_CMD_POWERDOWN_NORM
+  Also, return OPAL_BUSY_EVENT on failure sending FSP_CMD_REBOOT / DEEP_REBOOT.
+
+  We had a race condition between FSP Reset/Reload and powering down
+  the system from the host:
+
+  Roughly:
+
+  == ======================== ==========================================================
+  #  FSP                      Host
+  == ======================== ==========================================================
+  1  Power on
+  2                           Power on
+  3  (inject EPOW)
+  4  (trigger FSP R/R)
+  5                           Processes EPOW event, starts shutting down
+  6                           calls OPAL_CEC_POWER_DOWN
+  7  (is still in R/R)
+  8                           gets OPAL_INTERNAL_ERROR, spins in opal_poll_events
+  9  (FSP comes back)
+  10                          spinning in opal_poll_events
+  11 (thinks host is running)
+  == ======================== ==========================================================
+
+  The call to OPAL_CEC_POWER_DOWN is only made once as the reset/reload
+  error path for fsp_sync_msg() is to return -1, which means we give
+  the OS OPAL_INTERNAL_ERROR, which is fine, except that our own API
+  docs give us the opportunity to return OPAL_BUSY when trying again
+  later may be successful, and we're ambiguous as to if you should retry
+  on OPAL_INTERNAL_ERROR.
+
+  For reference, the linux code looks like this: ::
+
+    static void __noreturn pnv_power_off(void)
+    {
+            long rc = OPAL_BUSY;
+    
+            pnv_prepare_going_down();
+    
+            while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
+                    rc = opal_cec_power_down(0);
+                    if (rc == OPAL_BUSY_EVENT)
+                            opal_poll_events(NULL);
+                    else
+                            mdelay(10);
+            }
+            for (;;)
+                    opal_poll_events(NULL);
+    }
+
+  Which means that *practically* our only option is to return OPAL_BUSY
+  or OPAL_BUSY_EVENT.
+
+  We choose OPAL_BUSY_EVENT for FSP systems as we do want to ensure we're
+  running pollers to communicate with the FSP and do the final bits of
+  Reset/Reload handling before we power off the system.
+