On 14.09.2021 17:10, Roman Skakun wrote: > From: Roman Skakun <roman_skakun@xxxxxxxx> > > 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. > --- 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. > @@ -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