Re: [PATCH] swiotlb: set IO TLB segment size via cmdline
From: Jan Beulich <hidden>
Date: 2021-09-14 15:29:18
Also in:
linux-iommu, linux-mips, linuxppc-dev, lkml, xen-devel
On 14.09.2021 17:10, Roman Skakun wrote:
From: Roman Skakun <redacted> It is possible when default IO TLB size is not enough to fit a long buffers as described here [1]. This patch makes a way to set this parameter using cmdline instead of recompiling a kernel. [1] https://www.xilinx.com/support/answers/72694.html
I'm not convinced the swiotlb use describe there falls under "intended use" - mapping a 1280x720 framebuffer in a single chunk? (As an aside, the bottom of this page is also confusing, as following "Then we can confirm the modified swiotlb size in the boot log:" there is a log fragment showing the same original size of 64Mb.
quoted hunk ↗ jump to hunk
--- a/arch/mips/cavium-octeon/dma-octeon.c +++ b/arch/mips/cavium-octeon/dma-octeon.c@@ -237,7 +237,7 @@ void __init plat_swiotlb_setup(void) swiotlbsize = 64 * (1<<20); #endif swiotlb_nslabs = swiotlbsize >> IO_TLB_SHIFT; - swiotlb_nslabs = ALIGN(swiotlb_nslabs, IO_TLB_SEGSIZE); + swiotlb_nslabs = ALIGN(swiotlb_nslabs, swiotlb_io_seg_size());
In order to be sure to catch all uses like this one (including ones which make it upstream in parallel to yours), I think you will want to rename the original IO_TLB_SEGSIZE to e.g. IO_TLB_DEFAULT_SEGSIZE.
quoted hunk ↗ jump to hunk
@@ -81,15 +86,30 @@ static unsigned int max_segment; static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT; static int __init -setup_io_tlb_npages(char *str) +setup_io_tlb_params(char *str) { + unsigned long tmp; + if (isdigit(*str)) { - /* avoid tail segment of size < IO_TLB_SEGSIZE */ - default_nslabs = - ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE); + default_nslabs = simple_strtoul(str, &str, 0); } if (*str == ',') ++str; + + /* get max IO TLB segment size */ + if (isdigit(*str)) { + tmp = simple_strtoul(str, &str, 0); + if (tmp) + io_tlb_seg_size = ALIGN(tmp, IO_TLB_SEGSIZE);
From all I can tell io_tlb_seg_size wants to be a power of 2. Merely aligning to a multiple of IO_TLB_SEGSIZE isn't going to be enough. Jan