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xics: Add support for reduced priority field size

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This makes the ICS support less than the 8 architected bits
and sets the soc to use 3 bits by default.

All the supported bits set translates to "masked" (and will read
back at 0xff), any small value is used as-is.

Linux doesn't use priorities above 5, so this is a way to save
silicon. The number of supported priority bits is exposed to the
OS via the config register.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Benjamin Herrenschmidt 2020-06-22 23:38:34 +10:00
parent 5c2fc47e2c
commit bb54af59de
4 changed files with 71 additions and 31 deletions
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3
soc.vhdl
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@ -640,7 +640,8 @@ begin
xics_ics: entity work.xics_ics
generic map(
SRC_NUM => 16
SRC_NUM => 16,
PRIO_BITS => 3
)
port map(
clk => system_clk,

BIN
tests/test_xics.bin
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Binary file not shown.

24
tests/xics/xics.c
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@ -168,8 +168,8 @@ int xics_test_0(void)
assert(v0 = 0xff);
assert(v1 = 0xff);
ics_write_xive(0xaa, 0);
ics_write_xive(0x55, 1);
ics_write_xive(0xa, 0);
ics_write_xive(0x5, 1);
v0 = ics_read_xive(0);
v1 = ics_read_xive(1);
#ifdef DEBUG
@ -181,11 +181,15 @@ int xics_test_0(void)
print_number(v1);
puts("\n");
#endif
assert(v0 = 0xaa);
assert(v1 = 0x55);
assert(v0 = 0xa);
assert(v1 = 0x5);
ics_write_xive(0xff, 0);
ics_write_xive(0xff, 1);
v0 = ics_read_xive(0);
v1 = ics_read_xive(1);
assert(v0 = 0xff);
assert(v1 = 0xff);
return 0;
}
@ -198,28 +202,28 @@ int xics_test_1(void)
icp_write8(XICS_XIRR, 0x00); // mask all interrupts
// trigger two interrupts
potato_uart_irq_en(); // cause 0x500 interrupt
ics_write_xive(0x80, 0);
icp_write8(XICS_MFRR, 0x05); // cause 0x500 interrupt
potato_uart_irq_en(); // cause serial interrupt
ics_write_xive(0x6, 0); // set source to prio 6
icp_write8(XICS_MFRR, 0x04); // cause ipi interrupt at prio 5
// still masked, so shouldn't happen yet
delay();
assert(isrs_run == 0);
// unmask IPI only
icp_write8(XICS_XIRR, 0x40);
icp_write8(XICS_XIRR, 0x6);
delay();
assert(isrs_run == ISR_IPI);
// unmask UART
icp_write8(XICS_XIRR, 0xc0);
icp_write8(XICS_XIRR, 0x7);
delay();
assert(isrs_run == (ISR_IPI | ISR_UART));
// cleanup
icp_write8(XICS_XIRR, 0x00); // mask all interrupts
potato_uart_irq_dis();
ics_write_xive(0, 0);
ics_write_xive(0, 0xff);
isrs_run = 0;
return 0;

75
xics.vhdl
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@ -211,7 +211,8 @@ use work.wishbone_types.all;
entity xics_ics is
generic (
SRC_NUM : positive := 16
SRC_NUM : integer range 1 to 256 := 16;
PRIO_BITS : integer range 1 to 8 := 8
);
port (
clk : in std_logic;
@ -227,10 +228,12 @@ end xics_ics;
architecture rtl of xics_ics is
subtype pri_t is std_ulogic_vector(7 downto 0);
subtype pri_t is std_ulogic_vector(PRIO_BITS-1 downto 0);
type xive_t is record
pri : pri_t;
end record;
constant pri_masked : pri_t := (others => '1');
type xive_array_t is array(0 to SRC_NUM-1) of xive_t;
signal xives : xive_array_t;
@ -239,7 +242,7 @@ architecture rtl of xics_ics is
signal icp_out_next : ics_to_icp_t;
signal int_level_l : std_ulogic_vector(SRC_NUM - 1 downto 0);
function bswap(v : in std_ulogic_vector(31 downto 0)) return std_ulogic_vector is
function bswap(v : in std_ulogic_vector(31 downto 0)) return std_ulogic_vector is
variable r : std_ulogic_vector(31 downto 0);
begin
r( 7 downto 0) := v(31 downto 24);
@ -249,8 +252,35 @@ architecture rtl of xics_ics is
return r;
end function;
-- Register map
-- 0 : Config (currently hard wired base irq#)
function get_config return std_ulogic_vector is
variable r: std_ulogic_vector(31 downto 0);
begin
r := (others => '0');
r(23 downto 0) := std_ulogic_vector(to_unsigned(SRC_NUM, 24));
r(27 downto 24) := std_ulogic_vector(to_unsigned(PRIO_BITS, 4));
return r;
end function;
function prio_pack(pri8: std_ulogic_vector(7 downto 0)) return pri_t is
begin
return pri8(PRIO_BITS-1 downto 0);
end function;
function prio_unpack(pri: pri_t) return std_ulogic_vector is
variable r : std_ulogic_vector(7 downto 0);
begin
if pri = pri_masked then
r := x"ff";
else
r := (others => '0');
r(PRIO_BITS-1 downto 0) := pri;
end if;
return r;
end function;
-- Register map
-- 0 : Config
-- 4 : Debug/diagnostics
-- 800 : XIVE0
-- 804 : XIVE1 ...
@ -258,6 +288,7 @@ architecture rtl of xics_ics is
-- Config register format:
--
-- 23.. 0 : Interrupt base (hard wired to 16)
-- 27.. 24 : #prio bits (1..8)
--
-- XIVE register format:
--
@ -311,9 +342,9 @@ begin
int_level_l(reg_idx) &
'0' &
x"00000" &
xives(reg_idx).pri;
prio_unpack(xives(reg_idx).pri);
elsif reg_is_config = '1' then
be_out := std_ulogic_vector(to_unsigned(SRC_NUM, 32));
be_out := get_config;
elsif reg_is_debug = '1' then
be_out := x"00000" & icp_out_next.src & icp_out_next.pri;
end if;
@ -332,21 +363,22 @@ begin
if rising_edge(clk) then
if rst = '1' then
for i in 0 to SRC_NUM - 1 loop
xives(i) <= (pri => x"ff");
xives(i) <= (pri => pri_masked);
end loop;
elsif wb_valid = '1' and wb_in.we = '1' then
if reg_is_xive then
-- TODO: When adding support for other bits, make sure to
-- properly implement wb_in.sel to allow partial writes.
xives(reg_idx).pri <= be_in(7 downto 0);
report "ICS irq " & integer'image(reg_idx) & " set to:" & to_hstring(be_in(7 downto 0));
xives(reg_idx).pri <= prio_pack(be_in(7 downto 0));
report "ICS irq " & integer'image(reg_idx) &
" set to:" & to_hstring(be_in(7 downto 0));
end if;
end if;
end if;
end process;
-- generate interrupt. This is a simple combinational process,
-- potentially wasteul in HW for large number of interrupts.
-- potentially wasteful in HW for large number of interrupts.
--
-- could be replaced with iterative state machines and a message
-- system between ICSs' (plural) and ICP incl. reject etc...
@ -364,16 +396,19 @@ begin
-- A more favored than b ?
function a_mf_b(a: pri_t; b: pri_t) return boolean is
variable a_i : integer range 0 to 255;
variable b_i : integer range 0 to 255;
variable a_i : unsigned(PRIO_BITS-1 downto 0);
variable b_i : unsigned(PRIO_BITS-1 downto 0);
begin
a_i := to_integer(unsigned(a));
b_i := to_integer(unsigned(b));
return a < b;
a_i := unsigned(a);
b_i := unsigned(b);
report "a_mf_b a=" & to_hstring(a) &
" b=" & to_hstring(b) &
" r=" & boolean'image(a < b);
return a_i < b_i;
end function;
begin
-- XXX FIXME: Use a tree
max_pri := x"ff";
max_pri := pri_masked;
max_idx := 0;
for i in 0 to SRC_NUM - 1 loop
if int_level_l(i) = '1' and a_mf_b(xives(i).pri, max_pri) then
@ -381,11 +416,11 @@ begin
max_idx := i;
end if;
end loop;
if max_pri /= x"ff" then
report "MFI: " & integer'image(max_idx) & " pri=" & to_hstring(max_pri);
if max_pri /= pri_masked then
report "MFI: " & integer'image(max_idx) & " pri=" & to_hstring(prio_unpack(max_pri));
end if;
icp_out_next.src <= std_ulogic_vector(to_unsigned(max_idx, 4));
icp_out_next.pri <= max_pri;
icp_out_next.pri <= prio_unpack(max_pri);
end process;
end architecture rtl;