[U-Boot] [PATCH] spi: cadence_qspi_apb: Improve indirect write transaction

[Marek Vasut]

On 10/20/2016 01:01 PM, Vignesh R wrote:
> 
> 
> On Wednesday 19 October 2016 08:58 PM, Marek Vasut wrote:
>> On 10/19/2016 05:19 PM, Jagan Teki wrote:
>>> On Wed, Oct 19, 2016 at 8:18 PM, Marek Vasut <marex at denx.de> wrote:
>>>> On 10/19/2016 04:41 PM, Jagan Teki wrote:
>>>>> On Wed, Oct 19, 2016 at 10:10 AM, Vignesh R <vigneshr at ti.com> wrote:
>>>>>> Hi,
> ...
>>>>>>> You can probably pull this block from the else branch.
>>>>>>
>>>>>> Yeah, I guess writesb() can handle zero byte write request I believe.
>>>>>>
>>>>>> With above change, can I have your Acked-by/Reviewed-by?
>>>>>
>>>>> Also try to get the 'sf update' data before and after and append it on
>>>>> commit message.
>>>>
>>>> Why? Seems useless to me.
>>>
>>> Since it's a performance improvement patch better to have that
>>> numbers, no harm getting that data.
>>
>> Urghhhh, sf update is mixing multiple access patterns, it is by no means
>> a good performance metric for evaluating performance of the
>> write path.
>>
>> What you would need to do here is perform long unaligned writes
>> repeatedly (to eliminate outliers) and measure the improvement.
>> And you'd have to make sure the erase cycle is not counted in.
>>
>> I suspect the performance improvement would be negligible, but
>> I'd be happy to be proven wrong. If it'd be negligible, then
>> we should probably not complicate the code more and just drop
>> this patch.
>>
> 
> Today, I was performing unaligned writes of various sizes to get
> performance numbers and discovered that unaligned writes (i.e txbuf
> address is not word aligned or write_byte % 4 != 0) are sometimes
> failing on TI platforms with Cadence QSPI (with or w/o this patch) :(
> Reverting the patch "mtd: cqspi: Simplify indirect write code" seems to
> be helping. I don't see anything obviously wrong here. Let me debug
> whats causing the difference and get back.

Can you please drill into it ? I'd be happy to help testing.

-- 
Best regards,
Marek Vasut