Skip to content

L
linux
Switch branch/tag
  1. 04 Feb, 2011 3 commits
    • Stephen Boyd's avatar
      hvc_dcc: Simplify assembly for v6 and v7 ARM · 8e6d3fe1
      Stephen Boyd authored 
      The inline assembly differences for v6 vs. v7 in the hvc_dcc
driver are purely optimizations. On a v7 processor, an mrc with
the pc sets the condition codes to the 28-31 bits of the register
being read. It just so happens that the TX/RX full bits the DCC
driver is testing for are high enough in the register to be put
into the condition codes. On a v6 processor, this "feature" isn't
implemented and thus we have to do the usual read, mask, test
operations to check for TX/RX full.

Since we already test the RX/TX full bits before calling
__dcc_getchar() and __dcc_putchar() we don't actually need to do
anything special for v7 over v6. The only difference is in
hvc_dcc_get_chars(). We would test RX full, poll RX full, and
then read a character from the buffer, whereas now we will test
RX full, read a character from the buffer, and then test RX full
again for the second iteration of the loop. It doesn't seem
possible for the buffer to go from full to empty between testing
the RX full and reading a character. Therefore, replace the v7
versions with the v6 versions and everything works the same.
Acked-by: default avatarTony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: default avatarStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
      8e6d3fe1
    • Stephen Boyd's avatar
      hvc_dcc: Simplify put_chars()/get_chars() loops · bf73bd35
      Stephen Boyd authored 
      Casting and anding with 0xff is unnecessary in
hvc_dcc_put_chars() since buf is already a char[].
__dcc_get_char() can't return an int less than 0 since it only
returns a char. Simplify the if statement in hvc_dcc_get_chars()
to take this into account.

Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: default avatarStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
      bf73bd35
    • Stephen Boyd's avatar
      hvc_dcc: Fix bad code generation by marking assembly volatile · a9963201
      Stephen Boyd authored 
      Without marking the asm __dcc_getstatus() volatile my compiler
decides it can cache the value of __ret in a register and then
check the value of it continually in hvc_dcc_put_chars() (I had
to replace get_wait/put_wait with 1 and fixup the branch
otherwise my disassembler barfed on __dcc_(get|put)char).

00000000 <hvc_dcc_put_chars>:
   0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
   4:   e3a0c000        mov     ip, #0  ; 0x0
   8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
   c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
  10:   e3530000        cmp     r3, #0  ; 0x0
  14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
  18:   e7d1000c        ldrb    r0, [r1, ip]
  1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
  24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  28:   e28cc001        add     ip, ip, #1      ; 0x1
  2c:   e15c0002        cmp     ip, r2
  30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
  34:   e1a00002        mov     r0, r2
  38:   e12fff1e        bx      lr

As you can see, the value of the mrc is checked against
DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
Marking the asm volatile produces the following:

00000000 <hvc_dcc_put_chars>:
   0:   e3a03000        mov     r3, #0  ; 0x0
   4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
   8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
   c:   e3100202        tst     r0, #536870912  ; 0x20000000
  10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
  14:   e7d10003        ldrb    r0, [r1, r3]
  18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
  20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  24:   e2833001        add     r3, r3, #1      ; 0x1
  28:   e1530002        cmp     r3, r2
  2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
  30:   e1a00002        mov     r0, r2
  34:   e12fff1e        bx      lr

which looks better and actually works. Mark all the inline
assembly in this file as volatile since we don't want the
compiler to optimize away these statements or move them around
in any way.
Acked-by: default avatarTony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: default avatarStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
      a9963201
  3. 03 Feb, 2011 11 commits
  5. 01 Feb, 2011 1 commit
  7. 31 Jan, 2011 25 commits
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7