[PATCH] arc: make sure __delay() never gets executed with 0 loops

[Alexey Brodkin]

Current implementation of __delay() function uses so-called
zero-delay loops. And the only condition to exit that loop is
LP_COUNT (loop count register) = 1 (but not 0 as it might be easily
imagined).

So if our calculation of "loops" gives 0 (and that is pretty possible
given result of multiplication being >> 32) then zero-delay loop
mechanism starts with LP_COUNT=0 and it ends up decrementing LP_COUNT
while staying in the loop effectively producing close to infinite delay
instead of very short one.

I bumped into it with AXS101 + external DDR controller and caches
disabled. In that case I've got very small
loops_per_jiffy=0xf00:
>8
Calibrating delay loop... 0.77 BogoMIPS (lpj=3862)
>8

And on console output delays were way too long.

Signed-off-by: Alexey Brodkin 
Cc: Vineet Gupta 
 Please enter the commit message for your changes. Lines starting
---
 arch/arc/include/asm/delay.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/delay.h b/arch/arc/include/asm/delay.h
index 08e7e2a..1a7a1dc 100644
--- a/arch/arc/include/asm/delay.h
+++ b/arch/arc/include/asm/delay.h
@@ -57,7 +57,8 @@ static inline void __udelay(unsigned long usecs)
 */
loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
 
-   __delay(loops);
+   if (loops)
+   __delay(loops);
 }
 
 #define udelay(n) (__builtin_constant_p(n) ? ((n) > 2 ? __bad_udelay() \
-- 
2.4.3


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Re: [PATCH v9 2/2] pcie-designware platform driver

[Joao Pinto]

Hi Bjorn!
Did you have opportunity to check the v9 patch set?
Thanks.

Joao

On 2/10/2016 9:48 AM, Joao Pinto wrote:
> Hi Bjorn,
> 
> On 2/8/2016 11:28 PM, Bjorn Helgaas wrote:
>>>  if (!pci_has_flag(PCI_PROBE_ONLY)) {
>>>^
>>>drivers/pci/host/pcie-designware.c:581:20: note: each undeclared 
>>> identifier is reported only once for each function it appears in
>>>cc1: some warnings being treated as errors
>>
>> I have fixes for this on my pci/misc branch, so you don't need to
>> worry about these errors.  Basically I'm moving the PCI_PROBE_ONLY and
>> pci_has_flag() declarations from the arch-specific asm/pci-bridge.h
>> files to the generic linux/pci.h file.
> 
> Ok, thanks.
> 
>>
>>> vim +/pci_has_flag +581 drivers/pci/host/pcie-designware.c
>>>
>>> cbce7900 Zhou Wang   2015-10-29  575  
>>> cbce7900 Zhou Wang   2015-10-29  576  #ifdef CONFIG_ARM
>>> cbce7900 Zhou Wang   2015-10-29  577/* support old dtbs that 
>>> incorrectly describe IRQs */
>>> cbce7900 Zhou Wang   2015-10-29  578
>>> pci_fixup_irqs(pci_common_swizzle, of_irq_parse_and_map_pci);
>>> 0815f957 Yijing Wang 2014-11-11  579  #endif
>>> 0815f957 Yijing Wang 2014-11-11  580  
>>> cbce7900 Zhou Wang   2015-10-29 @581if 
>>> (!pci_has_flag(PCI_PROBE_ONLY)) {
>>> cbce7900 Zhou Wang   2015-10-29  582
>>> pci_bus_size_bridges(bus);
>>> cbce7900 Zhou Wang   2015-10-29  583
>>> pci_bus_assign_resources(bus);
>>> 4b1ced84 Jingoo Han  2013-07-31  584  
>>>
>>> :: The code at line 581 was first introduced by commit
>>> :: cbce7900598c26a12652f8ca9c41c5b29034c38d PCI: designware: Make 
>>> driver arch-agnostic
>>>
>>> :: TO: Zhou Wang 
>>> :: CC: Bjorn Helgaas 
>>>
>>> ---
>>> 0-DAY kernel test infrastructureOpen Source Technology 
>>> Center
>>> https://lists.01.org/pipermail/kbuild-all   Intel 
>>> Corporation
>>
>>
> 
> If there's anything else that is needed for the pcie-designware platform 
> driver,
> please let me know.
> 
> Thanks,
> Joao
> 


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