[Skiboot] [PATCH 4/4] FSP/CONSOLE: Fix fsp_console_write_buffer_space() call

[Ananth N Mavinakayanahalli]

On Sun, Sep 24, 2017 at 05:45:37PM +0000, Vasant Hegde wrote:
> Kernel calls fsp_console_write_buffer_space() to get console buffer
> availability. If there is enough buffer space then kernel will call
> fsp_console_write() to write actual console data.
> 
> In some extreeme corner cases (like one explained in commit c8a7535f)
> console becomes full and this function returns 0 to kernel (space available
> in console buffer < next incoming write size). Kernel will continue retrying
> until it gets enough space. So we will start seeing kernel RCU stalls.
> 
> This patch keeps track of previous available space. If previous space is
> same as current means, console is full and kernel is retrying. It may be due
> to very high console activity and slow response from FSP -OR- we may really
> have a issue. Hence lets return max console size so that kernel can make
> another try (calling fsp_console_write()) before actually dropping console
> write.
> 
> Signed-off-by: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>

Acked-by: Ananth N Mavinakayanahalli <ananth at linux.vnet.ibm.com>