[U-Boot] [PATCH 0/6] board: ti: am43xx: Enable hardware leveling

[Tero Kristo]

On 15/04/2019 11:56, Keerthy wrote:
> 
> 
> On 15/04/19 7:43 AM, keerthy wrote:
>>
>>
>> On 4/15/2019 6:35 AM, Tom Rini wrote:
>>> On Mon, Apr 15, 2019 at 06:19:31AM +0530, keerthy wrote:
>>>>
>>>>
>>>> On 4/13/2019 6:32 PM, Tom Rini wrote:
>>>>> On Fri, Apr 12, 2019 at 12:08:14PM +0530, Keerthy wrote:
>>>>>
>>>>>> The series adds the support for hardware leveling. This needs the
>>>>>> kernel to be patched with hardware leveling support and the
>>>>>> kernel support is already in linux-next:
>>>>>>
>>>>>> https://patchwork.kernel.org/project/linux-omap/list/?series=100273
>>>>>>
>>>>>> Match recommended values from EMIF Tools app note:
>>>>>> http://www.ti.com/lit/an/sprac70/sprac70.pdf
>>>>>
>>>>> What happens if you boot an old kernel with this series applied?  
>>>>> I'm a
>>>>> bit worried about applying something that breaks existing kernels,
>>>>> thanks!
>>>>
>>>> Hi Tom,
>>>>
>>>> Deep Sleep 0 feature will fail as the corresponding hardware leveling
>>>> patches will not be present.
>>>
>>> So to be clear, some new functionality will not work, but there is no
>>> functional regression?
>>
>> Okay i got your concern. Deep sleep 0 is currently working with 
>> software leveling that will stop working with this patch 
>> series(hardware leveling) applied on older kernels. EMIF tools 
>> application note recommends hardware leveling over what existed 
>> previously.
>>
>> Hence i posted this series. Older kernels with this patch series Deep 
>> sleep 0 feature will regress.
> 
> Tom,
> 
> We need hardware leveling as per EMIF document. So older kernels at best 
> can backport the patches here:
> 
> https://patchwork.kernel.org/patch/10882123/
> https://patchwork.kernel.org/patch/10882127/
> 
> I do not see any other way to enable hardware leveling.
> 
> Tero/Dave,
> 
> Any concerns?

Well, if we are to enable the feature, I can't see how we can avoid 
conflict with older kernels. However, most of the time I would say 
people upgrade their kernel before upgrading u-boot so this should be 
fine. If we are really worried, we could maybe add the support to kernel 
first, wait some time and merge the support to u-boot after that.

-Tero

> 
> Regards,
> Keerthy
>>
>>>
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