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

[Keerthy <j-keerthy@ti.com>]

On 15/04/19 4:58 PM, Tom Rini wrote:
> On Mon, Apr 15, 2019 at 12:22:22PM +0300, Tero Kristo wrote:
>> 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.
> 
> I assume that as the patches are working their way through -next now,
> we're also talking about older vendor tree kernels being where this did
> work?
> 

older kernels will have to port the above patches else Deep Sleep 0 will 
fail with newer u-boot with hardware leveling enabled. I assume they 
would be using older u-boot as well?