Re: [PATCH] watchdog: sbsa: use 32-bit read for WCV

[Robert Richter]

On 28.02.18 02:52:20, Jayachandran C wrote:
> According to SBSA spec v3.1 section 5.3:
>   All registers are 32 bits in size and should be accessed using
>   32-bit reads and writes. If an access size other than 32 bits
>   is used then the results are IMPLEMENTATION DEFINED.
>   [...]
>   The Generic Watchdog is little-endian
>
> The current code uses readq to read the watchdog compare register
> which does a 64-bit access. This fails on ThunderX2 which does not
> implement 64-bit access to this register.
>
> Fix this by using lo_hi_readq() that does two 32-bit reads.
>
> Signed-off-by: Jayachandran C 

Reviewed-by: Robert Richter 

I have looked into the non-atomic use of the register access and it
looks sane as the WCV register is only incremented by hardware. There
is no concurrent (write) access from the kernel.

-Robert

Re: [PATCH] watchdog: sbsa: use 32-bit read for WCV

[Guenter Roeck]

On 02/28/2018 02:52 AM, Jayachandran C wrote:

According to SBSA spec v3.1 section 5.3:
   All registers are 32 bits in size and should be accessed using
   32-bit reads and writes. If an access size other than 32 bits
   is used then the results are IMPLEMENTATION DEFINED.
   [...]
   The Generic Watchdog is little-endian

The current code uses readq to read the watchdog compare register
which does a 64-bit access. This fails on ThunderX2 which does not
implement 64-bit access to this register.

Fix this by using lo_hi_readq() that does two 32-bit reads.

Signed-off-by: Jayachandran C 


Reviewed-by: Guenter Roeck 


---
  drivers/watchdog/sbsa_gwdt.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c
index 316c2eb..e8bd988 100644
--- a/drivers/watchdog/sbsa_gwdt.c
+++ b/drivers/watchdog/sbsa_gwdt.c
@@ -50,6 +50,7 @@
   */
  
  #include 

+#include 
  #include 
  #include 
  #include 
@@ -159,7 +160,7 @@ static unsigned int sbsa_gwdt_get_timeleft(struct 
watchdog_device *wdd)
!(readl(gwdt->control_base + SBSA_GWDT_WCS) & SBSA_GWDT_WCS_WS0))
timeleft += readl(gwdt->control_base + SBSA_GWDT_WOR);
  
-	timeleft += readq(gwdt->control_base + SBSA_GWDT_WCV) -

+   timeleft += lo_hi_readq(gwdt->control_base + SBSA_GWDT_WCV) -
arch_counter_get_cntvct();
  
  	do_div(timeleft, gwdt->clk);