[PATCH 1/7] lmb: default LMB_LIMIT_DMA_BELOW_RAM_TOP for 64-bit Mediatek SoCs

[David Lechner]

On 6/12/26 12:52 PM, Sam Edwards wrote:
> On Fri, Jun 12, 2026 at 10:32 AM David Lechner <dlechner at baylibre.com> wrote:
>>
>> Add 64-bit Mediatek ARM SoCs to the default y setting of
>> LMB_LIMIT_DMA_BELOW_RAM_TOP. These platforms have a 4GiB DMA limit, e.g.
>> for the SD/MMC controller.
> 
> Hi David,
> 
> Is the 4GiB DMA limit due to the interconnect itself or are there
> merely a few blocks that can't speak 64-bit? If the latter, I think
> it'd be clearer to associate the setting with the culprit driver(s)
> rather than the whole platform, so that it can be removed if/when
> those drivers begin to use bounce buffers.
> 
For MediaTek, I think it is mostly specific IP blocks (e.g. MMC in the
mt8xxx targets in and NETSYS in mt79xx targets covered by this series are
the ones I am aware of).

Weijie Gao, maybe you have more information about this?