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Hermes SMTP Server) with ESMTPA ID a2add2a49fb2038e614f303f4cefd114; Fri, 02 Dec 2022 23:34:42 +0000 (UTC) From: Mark Millard Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable List-Id: Technical discussions relating to FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-hackers List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-hackers@freebsd.org Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3731.200.110.1.12\)) Subject: Does the RPi* DMA code in the kernel handle the distinctions between the 3 kinds of DMA engines? Message-Id: <18DF2CDD-3BC2-4100-9B8E-3BFD08F1F119@yahoo.com> Date: Fri, 2 Dec 2022 15:34:24 -0800 To: freebsd-arm , FreeBSD Hackers X-Mailer: Apple Mail (2.3731.200.110.1.12) References: <18DF2CDD-3BC2-4100-9B8E-3BFD08F1F119.ref@yahoo.com> X-Spamd-Result: default: False [-1.12 / 15.00]; SUBJECT_ENDS_QUESTION(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_MEDIUM(-1.00)[-0.998]; MV_CASE(0.50)[]; DMARC_POLICY_ALLOW(-0.50)[yahoo.com,reject]; NEURAL_SPAM_SHORT(0.37)[0.374]; R_SPF_ALLOW(-0.20)[+ptr:yahoo.com]; R_DKIM_ALLOW(-0.20)[yahoo.com:s=s2048]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_HAS_DN(0.00)[]; RCVD_IN_DNSWL_NONE(0.00)[98.137.69.148:from]; TO_MATCH_ENVRCPT_SOME(0.00)[]; DWL_DNSWL_NONE(0.00)[yahoo.com:dkim]; ASN(0.00)[asn:36647, ipnet:98.137.64.0/20, country:US]; MLMMJ_DEST(0.00)[freebsd-hackers@freebsd.org]; TO_DN_ALL(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; FREEMAIL_FROM(0.00)[yahoo.com]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_TRACE(0.00)[yahoo.com:+]; FROM_EQ_ENVFROM(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; FREEMAIL_ENVFROM(0.00)[yahoo.com]; RCVD_TLS_LAST(0.00)[]; RWL_MAILSPIKE_POSSIBLE(0.00)[98.137.69.148:from] X-Rspamd-Queue-Id: 4NP8Rv5THfz4YTc X-Spamd-Bar: - X-ThisMailContainsUnwantedMimeParts: N Does the RPi* DMA code in the kernel handle the distinctions between the 3 kinds of DMA engines? The engine types are named: DMA engine (30-bit DMA addressing: 1 GiByte, 256-bit burst space) DMA lite engine (only 128 bit burst space, no YLENGTH, TDMODE, S_STRIDE, D_STRIDE registsers, only 16 bits for DMA length (?_TXFR_LEN XLENGTH), no SRC_IGNORE or DEST_IGNORE modes, only about half the bandwidth of type DMA, uses ENABLE Regsiter 31:28 "PAGELITE" instead of 27:24 "PAGE" to control the "1G SDRAM ram page" used) DMA4 engine (not the same as dma4 of specific engines dma0..dma15; different register map offset pattern after ??_CB, more register map offsets than the other DMA types, 40 address bits with 40:32 in ??_SRCI/??_DESTI 7:0, ??_CB bits 31:0 are for Control Block Address 36:5, higher performance via "uncoupled read/write design", write burst capable, directly accesses the BCM2711 35-bit address bus so bypasses the paginging registers that are used for types DMA and DMA lite) The specific instances of engines (channels) have types: dma0 ..dma6 : Always type DMA (so far?) dma7 ..dma10: Always type DMA lite (so far?) dma11..dma14: Not the same for BCM2711: For BCM2711, type DMA4 Otherwise, type DMA lite (so far?) BCM2711 specific note: dma11 "is additionally able to access the PCIe interface". For reference, the live device tree for the BCM2711 has (examples from an 8 GiByte RPi4B): dma@7e007000 { compatible =3D "brcm,bcm2835-dma"; reg =3D <0x7e007000 0x00000b00>; interrupts =3D <0x00000000 0x00000050 0x00000004 = 0x00000000 0x00000051 0x00000004 0x00000000 0x00000052 0x00000004 = 0x00000000 0x00000053 0x00000004 0x00000000 0x00000054 0x00000004 = 0x00000000 0x00000055 0x00000004 0x00000000 0x00000056 0x00000004 = 0x00000000 0x00000057 0x00000004 0x00000000 0x00000057 0x00000004 = 0x00000000 0x00000058 0x00000004 0x00000000 0x00000058 0x00000004>; interrupt-names =3D "dma0", "dma1", "dma2", = "dma3", "dma4", "dma5", "dma6", "dma7", "dma8", "dma9", "dma10"; #dma-cells =3D <0x00000001>; brcm,dma-channel-mask =3D <0x000007f5>; phandle =3D <0x0000000b>; }; . . . dma@7e007b00 { compatible =3D "brcm,bcm2711-dma"; reg =3D <0x00000000 0x7e007b00 0x00000000 = 0x00000400>; interrupts =3D <0x00000000 0x00000059 0x00000004 = 0x00000000 0x0000005a 0x00000004 0x00000000 0x0000005b 0x00000004 = 0x00000000 0x0000005c 0x00000004>; interrupt-names =3D "dma11", "dma12", "dma13", = "dma14"; #dma-cells =3D <0x00000001>; brcm,dma-channel-mask =3D <0x00003000>; phandle =3D <0x00000040>; }; Note: dma15 "is exclusively used by the VPU" and I ignore it here. I ask, in part, because of: #define BCM_DMA_CH_MAX 12 that is used via the likes of: struct bcm_dma_ch sc_dma_ch[BCM_DMA_CH_MAX]; and: for (i =3D 0; i < BCM_DMA_CH_MAX; i++) { But the BCM2711 only has 0..10 defined for brcm,bcm2835-dma in its device live device tree, although brcm,dma-channel-mask allows avoiding what is missing. 11..14 are defined in brcm,bcm2711-dma instead --but the code makes no use of it, given the brcm,bcm2835-dma's brcm,dma-channel-mask. But/also, the brcm,bcm2835-dma's brcm,dma-channel-mask includes examples of both "DMA engine" and "DMA lite engine", so still leading to some distinctions that should be made. So far, I've not been able to identify code/data making any distinctions for the likes of dma7..dma14 beyond what brcm,dma-channel-mask completely avoids. Note: So far as I can tell, the PCIe bus-mastering that is associated with the XHCI in the BCM2711 is separate from the above. The "B0T" BCM2711 parts have a 3 GiByte limitation just for this PCIe bus-mastering(/XHCI) and the "C0T" BCM2711 parts no longer are limited to a subset of the available RAM for PCIe bus-mastering(/XHCI). Examples from 8 GiByte RPi4B's: dma-ranges =3D <0x02000000 0x00000004 0x00000000 = 0x00000000 0x00000000 0x00000000 0xc0000000>; vs. dma-ranges =3D <0x02000000 0x00000004 0x00000000 = 0x00000000 0x00000000 0x00000002 0x00000000>; So, XHCI related bounce buffering could be avoided on=20 "C0T" parts. For BCM2711 "B0T" vs. "C0T" there is also emmc2bus with: dma-ranges =3D <0x00000000 0xc0000000 0x00000000 = 0x00000000 0x40000000>; (so: matching the soc dma-ranges, other than the #of = cells for holding the 1st addr) vs. dma-ranges =3D <0x00000000 0x00000000 0x00000000 = 0x00000000 0xfc000000>; (so not matching the soc dma-ranges) emmc2bus contains: emmc2@7e340000 { compatible =3D "brcm,bcm2711-emmc2"; . . . which looks to mean that the dma_ranges for brcm,bcm2711-emmc2 changed to not match the soc dma-ranges. I've not noticed any code/data that would track this change. I do not know the implications of the difference for what FreeBSD's code does --or if FreeBSD ever tries to use the brcm,bcm2711-emmc2 . =3D=3D=3D Mark Millard marklmi at yahoo.com