[U-Boot] [v2 2/6] spi: cadence_qspi: remove sram polling from flash read

[vikas]

Hi Marek,

On 08/13/2015 03:47 PM, Marek Vasut wrote:
> On Thursday, August 13, 2015 at 11:04:59 PM, vikas wrote:
>> Hi Marek,
> 
> Hi!
> 
>> On 08/13/2015 01:35 PM, Marek Vasut wrote:
>>> On Thursday, August 13, 2015 at 09:49:49 PM, vikas wrote:
>>>
>>> Hi!
>>>
>>>>>> On 08/12/2015 07:09 PM, Marek Vasut wrote:
>>>>>>> On Thursday, July 16, 2015 at 04:27:30 AM, Vikas Manocha wrote:
>>>>>>>> There is no need to check for sram fill level. If sram is empty, cpu
>>>>>>>> will go in the wait state till the time data is available from
>>>>>>>> flash.
>>>>>>>
>>>>>>> Consider the following scenario:
>>>>>>> - CPU core reads some memory area, but there are no data available
>>>>>>> just yet
>>>>>>>
>>>>>>>   => CPU core goes into wait state
>>>>>>>
>>>>>>> - The data never arrive
>>>>>>>
>>>>>>> Will the CPU be stuck forever ? If we checked the fill level first
>>>>>>> instead, we would never enter such stuck-state.
>>>>>>
>>>>>> This indirect mode of reading/writing would be entered when the
>>>>>> read/write addresses are in the programmed valid range of addresses.
>>>>>>
>>>>>> Even in case of "data never arrive" scenario, a simple timeout seems
>>>>>> better then currently implemented read sram level with timeout.
>>>>>
>>>>> How do you implement a "simple timeout" if the CPU core is stuck and
>>>>> does not execute instructions ? If you mean interrupt, then forget it,
>>>>> U-Boot does not do interrupts ;-)
>>>>
>>>> Oh yes, you are right.
>>>
>>> So shall we keep the SRAM piece ?
>>
>> Although in this case the better solution would be to have watermark
>> interrupt/status check based on sram fill level, let us keep the existing
>> piece of SRAM.
> 
> Good.
> 
>> Can we make it configurable (SRAM Level test or not) like from DT or
>> #define ?
> 
> How would you call such an option ? Something like CONFIG_SYS_YOLO (to indicate
> that life is too short to use correct, but slower code) ? :-)
> 
> I don't want to have two different codepaths in the codebase, one of which is
> buggy. So no, I disagree we should add this option. I also don't think it would
> be such a performance improvement, so I only see downsides in such a code.

I expected the same answer :-) & agree also.
ok, the issue is SRAM Fill Level register is not being updated on my SOC, seems like design issue.
Any idea how can i add this fix (to avoid sram level polling) to my soc in u-boot mainline.

Rgds,
Vikas

> 
> Best regards,
> Marek Vasut
> .
>