Re: [PATCH v1 7/7] mci: imx-esdhc: support DMA in the i.MX8M PBL eMMC loader

Hoi Sascha,


> On 2026-06-27 19:43, Johannes Schneider wrote:
> > The PBL eMMC loader was hardwired to PIO via esdhc_use_pio_mode(): IN_PBL
> > forced PIO unconditionally. PIO is slow -- on an i.MX8MM board loading the
> > ~1.6 MB next stage took ~559 ms; SDMA/ADMA2 do it in ~21 ms.
>
> For proper DMA support you'll need memory synchronization in form of dma_map_*
> or dma_sync_* helpers which we do not have in PBL. Without them it won't
> work with MMU enabled.

Noted. So since the MMU is still left as it is = off were still good wtih the
current sdma/adma implementation. But maybe worth a comment in the code/commit?

> Have you tried enabling the MMU in the mean time? This
> should give you decent performance even with PIO.
>
> Sascha
>

Thanks for the hint/idea!
I've let the AI draft a PIO+MMU-on change and ran a round of measurements,
(Caveat: sample size is one) there is some gain - but we get more with SDMA or ADMA
And interestingly "the same" with the later two.:

 Phase                  PIO   PIO+MMU   SDMA   ADMA2
--------------------------------------------------------------------
 BootROM                  1       1       1        2
 PBL-init                 3       3       3        3
 DDR-training           265     265     262      269
 PBL-load (total)       884     413     257      258
   PBL-pre-load         165     170     166      167
   load_bl33            713     241      86       85
   PBL-post-load          5       1       5        5
 BL31-early             114     114     114      114
 BL31-platform           16      15      15       15
 BL31-runtime            98      98      98       98
--------------------------------------------------------------------
 time-to-barebox       1393     921     763      770


If you want i can brush up that PIO+MMU code and send it out too.


gruß
Johannes