Messages in this thread | | | Date | Fri, 26 Feb 2016 17:31:53 +0100 | Subject | Re: [PATCH] mtd: bcm47xxsflash: use ioremap_cachable() instead of KSEG0ADDR() | From | Rafał Miłecki <> |
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On 26 February 2016 at 15:18, Maciej W. Rozycki <macro@imgtec.com> wrote: > On Fri, 26 Feb 2016, Rafał Miłecki wrote: > >> >> KSEG0ADDR was translating 0x1c000000 into 0x9c000000. With >> >> ioremap_cachable we use MIPS's __ioremap (and remap_area_pages). This >> >> results in different address (e.g. 0xc0080000) but it still should be >> >> cached as expected and it was successfully tested with BCM47186B0. >> > >> > This is due to this piece: >> > >> > /* >> > * Map uncached objects in the low 512mb of address space using KSEG1, >> > * otherwise map using page tables. >> > */ >> > if (IS_LOW512(phys_addr) && IS_LOW512(last_addr) && >> > flags == _CACHE_UNCACHED) >> > return (void __iomem *) CKSEG1ADDR(phys_addr); >> > >> > special-casing uncached mapping only (replicated in 2 places). I think >> > there will really be no harm from returning a KSEG0 mapping for calls >> > requesting a caching mode equal to `_page_cachable_default', which -- >> > depending on the cache architecture -- will have been either hardwired or >> > prearranged via Config.K0. I think there's really no need to put pressure >> > on the TLB, which may be small, in cases where a fixed mapping will do. >> >> No, it isn't hitting condition you pointed. We call ioremap_cachable >> which uses _page_cachable_default as a flag. This flag >> (_page_cachable_default) isn't equal to the _CACHE_UNCACHED. > > That's exactly what I wrote: code I quoted is "special-casing uncached > mapping only" -- which as you have correctly observed does not apply after > your change anymore. Which is why previously you got an address in the > unmapped KSEG1 segment and now you get an address in the mapped KSEG2 > rather than the unmapped KSEG0 segment. > >> Moreover code you pointed uses CKSEG1ADDR which would result in >> setting bit KSEG1 (0xa0000000). As I pointed in the commit message >> address it ORed with KSEG2 (0xc0000000). > > It's not merely ORed, it's actually mapped via the TLB. > > I hope this makes things clear.
Ah, sorry, I missed the point of your explanation. Now it's clear, thanks!
-- Rafał
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