Hi, > -----Original Message----- > From: Stephen Warren <swar...@wwwdotorg.org> > Sent: Tuesday, August 27, 2019 7:50 PM > To: Vikas MANOCHA <vikas.mano...@st.com>; Tom Rini > <tr...@konsulko.com> > Cc: twar...@wwwdotorg.org; u-boot@lists.denx.de; Stephen Warren > <swar...@nvidia.com> > Subject: Re: [PATCH] board_f: fix noncached reservation calculation > > On 8/27/19 6:01 PM, Vikas MANOCHA wrote: > > Stephen Warren wrote at Tuesday, August 27, 2019 3:50 PM > >> On 8/27/19 4:10 PM, Vikas MANOCHA wrote: > >>> Stephen Warren wrote at Tuesday, August 27, 2019 10:55 AM > >>>> The current code in reserve_noncached() has two issues: > >>>> > >>>> 1) The first update of gd->start_addr_sp always rounds down to a > >>>> section start. However, the equivalent calculation in > >>>> cache.c:noncached_init() always first rounds up to a section start, > >>>> then subtracts a section size. > >>>> These two calculations differ if the initial value is already > >>>> rounded to section alignment. > >>> > >>> It shouldn't cause any issue, first one round down to section size. > >>> Second > >>> one(cache.c: noncached_init()) rounds up, so needs section size > >>> subtraction. > >> > >> Here's an example where it fails, based on code before my patch: > >> > >> Assume that MMU section size is 2, and that mem_malloc_start and > >> gd->start_addr_sp are both 1000M on entry to the functions, and the > >> noncached region is 1 (what Jetson TX1 uses). The example uses values > >> assumed to be multiples of 1M to make the numbers easier to read. > >> > >> noncached_init: > >> > >> // mem_malloc_start = 1000 > >> end = ALIGN(mem_malloc_start, MMU_SECTION_SIZE) - > MMU_SECTION_SIZE; > >> // end = 1000 - 2 = 998 // was already aligned, so 1000 not 1002 size > >> = ALIGN(CONFIG_SYS_NONCACHED_MEMORY, > >> MMU_SECTION_SIZE); // size = 2 start = end - size; // start = 998 - 2 > >> = 996 // region is 996...998 > > > > Thanks for this example, it definitely seems a bug. Just that we are > > fixing it > by adding this gap in the reserve_noncached() also. > > Better would be to fix this subtraction of MMU_SECTION_SIZE by aligning > down "end" location, like: > > > > end = ALIGN_DOWN(mem_malloc_start, MMU_SECTION_SIZE); // end = > 1000 > > size = ALIGN(CONFIG_SYS_NONCACHED_MEMORY, MMU_SECTION_SIZE); > // size = > > 2 start = end -size; // start = 998 > > That would change yet another piece of code that's been stable for a while. > It's late in the U-Boot release cycle, so I think we should be conservative, > and > not change any more code than necessary. Changing lots of extra code > would run the risk of introducing more regressions. I'd rather (a) apply the > original change I posted, which adjusts only the code that caused the > regression, or (b) revert the patch that caused the regression.
Ok, Either way is fine. > > If you want to adjust the code in noncached_init, we can do that > immediately after the release, to give maximum time for any regressions to > be debugged and fixed before the next release. Ok. Cheers, Vikas _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
