Re: [PATCH 04/17 v1] irqchip: Add driver for IXP4xx
From: khalasa@piap.pl (Krzysztof Hałasa)
Date: 2019-02-20 07:35:41
Arnd Bergmann [off-list ref] writes:
quoted hunk
- the MMIO workarounds don't really work for a VGA card in general since you cannot map the frame buffer into user space, so the application of that is still a bit limited. I suspect you would have had the same problem with the existing ixp4xx code as well, depending on how the driver implements user space graphics.
Right. Now I remember I put the VGA FB in the first 64 MB of PCI address space (this means it was a 64 MB VGA, and that I could actually do direct and indirect accesses at the same time). The rest of PCI address space was used indirectly for (I guess) VGA registers and other hardware (SATA controller and similar stuff - nothing which would require mapped PCI memory). The PCI bus mastering limitation was far worse - there are boards with 128 and 256 MB (maximum possible on IXP42x) of RAM and double SKB buffering with e.g. dual gigabit Ethernet wasn't nice. I ended up with a hack which allocated network buffers from the first 64 MB of RAM only. -- Krzysztof Halasa Industrial Research Institute for Automation and Measurements PIAP Al. Jerozolimskie 202, 02-486 Warsaw, Poland _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel