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Re: [PATCH V16 09/12] MIPS: Loongson: Add Loongson-3 Kconfig options

To: Huacai Chen <chenhc@lemote.com>
Subject: Re: [PATCH V16 09/12] MIPS: Loongson: Add Loongson-3 Kconfig options
From: Aurelien Jarno <aurelien@aurel32.net>
Date: Mon, 13 Jan 2014 05:30:26 +0100
Cc: Alex Smith <alex.smith@imgtec.com>, Ralf Baechle <ralf@linux-mips.org>, John Crispin <john@phrozen.org>, "Steven J. Hill" <Steven.Hill@imgtec.com>, linux-mips@linux-mips.org, Fuxin Zhang <zhangfx@lemote.com>, Zhangjin Wu <wuzhangjin@gmail.com>, Hongliang Tao <taohl@lemote.com>, Hua Yan <yanh@lemote.com>
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On Mon, Jan 13, 2014 at 11:02:19AM +0800, Huacai Chen wrote:
> On Sat, Jan 11, 2014 at 11:24 PM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> > On Thu, Jan 09, 2014 at 01:07:30PM +0000, Alex Smith wrote:
> >> On 08/01/14 02:44, Huacai Chen wrote:
> >> >Added Kconfig options include: Loongson-3 CPU and machine definition,
> >> >CPU cache features, UEFI-like firmware interface (LEFI), HT-linked PCI,
> >> >and big memory support.
> >> >
> >> >Signed-off-by: Huacai Chen <chenhc@lemote.com>
> >> >Signed-off-by: Hongliang Tao <taohl@lemote.com>
> >> >Signed-off-by: Hua Yan <yanh@lemote.com>
> >> >---
> >> >  arch/mips/Kconfig           |   29 +++++++++++++++++++++++++++-
> >> >  arch/mips/loongson/Kconfig  |   44 
> >> > +++++++++++++++++++++++++++++++++++++++++++
> >> >  arch/mips/loongson/Platform |    1 +
> >> >  3 files changed, 73 insertions(+), 1 deletions(-)
> >> >
> >> >diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> >> >index 17cc7ff..513e941 100644
> >> >--- a/arch/mips/Kconfig
> >> >+++ b/arch/mips/Kconfig
> >> >@@ -1487,6 +1487,18 @@ config CPU_LOONGSON2
> >> >     select CPU_SUPPORTS_HIGHMEM
> >> >     select CPU_SUPPORTS_HUGEPAGES
> >> >
> >> >+config CPU_LOONGSON3
> >> >+    bool "Loongson 3 CPU"
> >> >+    depends on SYS_HAS_CPU_LOONGSON3
> >> >+    select CPU_SUPPORTS_64BIT_KERNEL
> >> >+    select CPU_SUPPORTS_HIGHMEM
> >> >+    select CPU_SUPPORTS_HUGEPAGES
> >> >+    select WEAK_ORDERING
> >> >+    select WEAK_REORDERING_BEYOND_LLSC
> >> >+    help
> >> >+            The Loongson 3 processor implements the MIPS III instruction 
> >> >set
> >> >+            with many extensions.
> >> >+
> >>
> >> This should be moved into the "CPU type" choice block. Currently
> >> this appears as an option outside of that choice, and so it is
> >> possible to build a kernel without any CPU type selected.
> >>
> >> Also, as Aurelien said on the previous version, shouldn't the
> >> comment be changed to MIPS64R2 rather than MIPS III even if you
> >> aren't selecting the MIPS64 CPU types for the time being? Note, if
> >> you replied to that comment I may not have seen it - I think the
> >> list is filtering your replies because they're HTML emails.
> >>
> >> >  config CPU_LOONGSON1
> >> >     bool
> >> >     select CPU_MIPS32
> >> >@@ -1513,6 +1526,10 @@ config SYS_HAS_CPU_LOONGSON2F
> >> >     select CPU_SUPPORTS_ADDRWINCFG if 64BIT
> >> >     select CPU_SUPPORTS_UNCACHED_ACCELERATED
> >> >
> >> >+config SYS_HAS_CPU_LOONGSON3
> >> >+    bool
> >> >+    select CPU_SUPPORTS_CPUFREQ
> >> >+
> >> >  config SYS_HAS_CPU_LOONGSON1B
> >> >     bool
> >> >
> >> >@@ -1703,7 +1720,7 @@ choice
> >> >
> >> >  config PAGE_SIZE_4KB
> >> >     bool "4kB"
> >> >-    depends on !CPU_LOONGSON2
> >> >+    depends on !CPU_LOONGSON2 && !CPU_LOONGSON3
> >> >     help
> >> >      This option select the standard 4kB Linux page size.  On some
> >> >      R3000-family processors this is the only available page size.  Using
> >> >@@ -2373,6 +2390,16 @@ config PCI
> >> >       your box. Other bus systems are ISA, EISA, or VESA. If you have 
> >> > PCI,
> >> >       say Y, otherwise N.
> >> >
> >> >+config HT_PCI
> >> >+    bool "Support for HT-linked PCI"
> >> >+    depends on CPU_LOONGSON3
> >> >+    select PCI_DOMAINS
> >> >+    help
> >> >+      Loongson family machines use Hyper-Transport bus for inter-core
> >> >+      connection and device connection. The PCI bus is a subordinate
> >> >+      linked at HT. Choose Y unless you are using Loongson 2E/2F based
> >> >+      machines.
> >> >+
> >>
> >> Should this default to y, given that it is selected in the
> >> defconfig? Also, the comment referring to 2E/2F is redundant given
> >> that it depends on CPU_LOONGSON3 and cannot be selected on those
> >> machines.
> >
> > I am still not sure we need such an option. This option only changes an
> > address in arch/mips/include/asm/mach-loongson/loongson.h:
> >
> > | #if defined(CONFIG_HT_PCI)
> > | #define LOONGSON_PCIIO_BASE     loongson_sysconf.pci_io_base
> > | #else
> > | #define LOONGSON_PCIIO_BASE     0x1fd00000
> > | #endif
> >
> > If both options are working on a Loongson 3 machine, it's definitely a
> > good idea to leave the choice to the user. That said if only the address
> > from loongson_sysconf.pci_io_base works on a Loongson 3 machine, this
> > option must always be selected and is therefore useless.
> HT_PCI is needed, because Loongson-3 device structure looks like this:
> Loongson3-Core -----       ---- MEM
>          |--- Cache ---|
> HT1-controller  -------       ---- PCI-Controller --- PCI-Devices (PATH-B)
>     |
>     |
>  PCI-Controller
>     |
>     |
>  PCI-Devices (PATH-A)
> 
> If PCI devices are linked via PATH-A, we should select HT_PCI;
> otherwise we should unselected HT_PCI.

Thanks for the explanation, it looks now more clear why we need this
option. Both cases are valid, it just depends on where the PCI
controller is connected.

That said it means that we won't be able to use the same kernel on
machines using the PATH-A and on machines using the PATH-B. Is there
a way to determine this at runtime through LEFI?

Aurelien

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net

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