Date: Wed, 30 Sep 2020 15:40:06 -0700 From: Mark Millard <marklmi@yahoo.com> To: Robert Crowston <crowston@protonmail.com> Cc: freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: RPi4B's DMA11 (DMA4 engine example) vs. xHCI/pcie Message-ID: <93A90975-39F1-4DA3-87E0-89E07505108A@yahoo.com> In-Reply-To: <tNJ_d5vRy5yTyYQw2MoZvybqy_7lqaHUfmXjedMUax0-LUolwajbPIPJLpQZqV6e9ymgkUogKFKRv0E0LrfDmLMiE99QraRHPamDyMDPVm4=@protonmail.com> References: <8C6DE44F-6CE2-4C74-8748-3BBFB54AE183@yahoo.com> <0FE382AB-8DE3-4467-9CB0-E8582AC70EA2@yahoo.com> <85FEDC51-B5B0-4ED4-A5ED-62B63EF9D5A8@yahoo.com> <B440C8D8-AA02-49E4-A0D6-3EA9B7FFD13A@yahoo.com> <903FE769-ED46-4FBC-A272-4D2C89A9CD7A@yahoo.com> <tNJ_d5vRy5yTyYQw2MoZvybqy_7lqaHUfmXjedMUax0-LUolwajbPIPJLpQZqV6e9ymgkUogKFKRv0E0LrfDmLMiE99QraRHPamDyMDPVm4=@protonmail.com>
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On 2020-Sep-30, at 14:15, Robert Crowston <crowston at protonmail.com> = wrote: > Very interesting analysis. Certainly uncovered a few things I wasn't = aware of. >=20 > By default sc->sc_bus.dma_bits in xhci_init is 64 bits; I toggle it = back to 32 bits in the xhci shim I wrote for the Pi 4. You can see that = output in a verbose dmesg. >=20 My biggest worry from all that material, for things as they currently are, is that it appears that FreeBSD could try to use a RPi4B DMA LITE engine but not follow its limitations when doing so. For example, ending up using a smaller size DMA transfer than intended (just 16 bits for size). (Other RPi's might have the same issue?) =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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