Date: Fri, 28 Jul 2023 19:47:08 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 272780] genet: General question of DMA alignment requirement for tx/rx_buf Message-ID: <bug-272780-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272780 Bug ID: 272780 Summary: genet: General question of DMA alignment requirement for tx/rx_buf Product: Base System Version: CURRENT Hardware: arm OS: Any Status: New Severity: Affects Some People Priority: --- Component: bin Assignee: bugs@FreeBSD.org Reporter: jiahali@blackberry.com Hi, Is there a DMA alignment requirement for genet driver's TX/RX buffer? In gen_bus_dma_init(), genet driver requires the TX/RX buffer to be 4 bytes aligned. However, gen_newbuf_rx() fetches a mbuf cluster, then trims the first two bytes of the mbuf cluster. My understanding is that the RX buffer will be 2 bytes aligned but might not be 4 bytes aligned. I understand that the DMA stack will handle this misalignment using something like a bounce buffer. Since there isn't a document for the bcm ethernet controller online, I am curious about the reason why genet driver does not enforce the allocated mbuf to be 4 bytes aligned. In TX, genet driver does not know the starting address of mbuf passed from the upper layer. Is it possible that the genet driver is also compatible with other alignment constraints, like 1, 2, or 32 byte(s)? Thanks, Jiahao -- You are receiving this mail because: You are the assignee for the bug.help
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