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Date: Wed, 08 Oct 2014 12:24:50 -0400 (EDT) From: David Miller <davem@...emloft.net> To: moshel@....mellanox.co.il Cc: ogerlitz@...lanox.com, jackm@....mellanox.co.il, talal@...lanox.com, yevgenyp@...lanox.com, netdev@...r.kernel.org, amirv@...lanox.com Subject: Re: [PATCH V1 net-next 1/2] pgtable: Add API to query if write combining is available From: Moshe Lazer <moshel@....mellanox.co.il> Date: Wed, 08 Oct 2014 11:44:57 +0300 >> #if defined(__i386__) || defined(__x86_64__) >> if (map->type == _DRM_REGISTERS && !(map->flags & _DRM_WRITE_COMBINING)) >> tmp = pgprot_noncached(tmp); >> else >> tmp = pgprot_writecombine(tmp); >> #elif defined(__powerpc__) >> pgprot_val(tmp) |= _PAGE_NO_CACHE; >> if (map->type == _DRM_REGISTERS) >> pgprot_val(tmp) |= _PAGE_GUARDED; >> #elif defined(__ia64__) >> if (efi_range_is_wc(vma->vm_start, vma->vm_end - >> vma->vm_start)) >> tmp = pgprot_writecombine(tmp); >> else >> tmp = pgprot_noncached(tmp); >> #elif defined(__sparc__) || defined(__arm__) || defined(__mips__) >> tmp = pgprot_noncached(tmp); >> #endif > The idea was to provide an indication as for whether the arch supports > write-combining in general. > If we want to benefit from blue flame operations, we need to map the > blue flame registers as write combining - otherwise there is no > benefit. So we would like to know if write combining is supported by > the system or not. > You completely miss my point. On a given architectuire it might be _illegal_ to map certain address ranges as write-combining without checks like the ones above that ia64 needs. Therefore your proposed interface is by definition insufficient. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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