On Fri, Jun 12, 2026 at 3:13 PM David Lechner <[email protected]> wrote: > > On 6/12/26 4:30 PM, David Lechner wrote: > > On 6/12/26 12:52 PM, Sam Edwards wrote: > >> On Fri, Jun 12, 2026 at 10:32 AM David Lechner <[email protected]> > >> 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? > > > > > > Sam, > > Just to make sure I understood you correctly, your suggestion is to > do this instead?
Yep -- to me, that says "this driver currently has broken 64-bit DMA" rather than "this platform can't ever tolerate 64-bit allocations." > --- > diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig > index 24bd16ad5f3..e2c5a54f925 100644 > --- a/drivers/mmc/Kconfig > +++ b/drivers/mmc/Kconfig > @@ -858,6 +858,7 @@ config MMC_MTK > bool "MediaTek SD/MMC Card Interface support" > depends on ARCH_MEDIATEK || ARCH_MTMIPS || ARCH_AIROHA > depends on OF_CONTROL > + select LMB_LIMIT_DMA_BELOW_RAM_TOP > help > This selects the MediaTek(R) Secure digital and Multimedia card > Interface. > If you have a machine with a integrated SD/MMC card reader, say Y > here. > diff --git a/drivers/net/mtk_eth/Kconfig b/drivers/net/mtk_eth/Kconfig > index 5d4e54ab90e..7d58f542bde 100644 > --- a/drivers/net/mtk_eth/Kconfig > +++ b/drivers/net/mtk_eth/Kconfig > @@ -5,6 +5,7 @@ config MEDIATEK_ETH > select PHYLIB > select DM_GPIO > select DM_RESET > + select LMB_LIMIT_DMA_BELOW_RAM_TOP > help > This Driver support MediaTek Ethernet GMAC > Say Y to enable support for the MediaTek Ethernet GMAC. > diff --git a/lib/Kconfig b/lib/Kconfig > index 27ad43125e4..cf13ac1bdad 100644 > --- a/lib/Kconfig > +++ b/lib/Kconfig > @@ -1298,7 +1298,7 @@ config SPL_LMB_ARCH_MEM_MAP > config LMB_LIMIT_DMA_BELOW_RAM_TOP > bool > depends on LMB > - default y if ARCH_BCM283X || (ARCH_MEDIATEK && ARM64) > + default y if ARCH_BCM283X > help > Some architectures can not DMA above ram_top boundary, > which is after 4 GiB or 32-bit boundary too. Limit the >
