spi: Send dummy clocks at boot

When using an FPGA which routes the SPI clock via STARTUPE2 as is
done on the Nexys Video (or optionally on Arty), the HW needs at
least 3 beats of that clock to complete the switch from the internal
config clock to the one we provide.

This works around it by having the SPI controller send 8 dummy
clocks at boot time with CS held high.

Without this, flash identification will fail those boards

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

spi_flash_ctrl.vhdl

@@ -11,6 +11,9 @@ entity spi_flash_ctrl is
         DEF_CLK_DIV     : natural  := 2;      -- Clock divider SCK = CLK/((CLK_DIV+1)*2)
         DEF_QUAD_READ   : boolean  := false;  -- Use quad read with 8 clk dummy
 
+        -- Dummy clocks after boot
+        BOOT_CLOCKS     : boolean  := true;   -- Send 8 dummy clocks after boot
+
         -- Number of data lines (1=MISO/MOSI, otherwise 2 or 4)
         DATA_LINES      : positive := 1
         );
@@ -103,7 +106,7 @@ architecture rtl of spi_flash_ctrl is
     constant DEFAULT_CS_TIMEOUT : integer := 32;
 
     -- Automatic mode state
-    type auto_state_t is (AUTO_IDLE, AUTO_CS_ON, AUTO_CMD,
+    type auto_state_t is (AUTO_BOOT, AUTO_IDLE, AUTO_CS_ON, AUTO_CMD,
                           AUTO_ADR0, AUTO_ADR1, AUTO_ADR2, AUTO_ADR3,
                           AUTO_DUMMY,
                           AUTO_DAT0, AUTO_DAT1, AUTO_DAT2, AUTO_DAT3,
@@ -125,7 +128,7 @@ architecture rtl of spi_flash_ctrl is
     -- Automatic mode latches
     signal auto_data      : std_ulogic_vector(wb_out.dat'left downto 0) := (others => '0');
     signal auto_cnt       : integer range 0 to 63 := 0;
-    signal auto_state     : auto_state_t := AUTO_IDLE;
+    signal auto_state     : auto_state_t := AUTO_BOOT;
     signal auto_last_addr : std_ulogic_vector(31 downto 0);
 
 begin
@@ -176,7 +179,7 @@ begin
             -- in practice.
             --
             if cmd_valid = '1' and cmd_ready = '1' then
-                pending_read <= '1';
+                pending_read <= not wb_req.we;
             elsif bus_idle = '1' then
                 pending_read <= '0'; 
             end if;
@@ -396,21 +399,29 @@ begin
         if rst = '1' or ctrl_reset = '1' then
             auto_cs <= '0';
             auto_cnt_next <= 0;
-            auto_next <= AUTO_IDLE;
+            auto_next <= AUTO_BOOT;
         else
             -- Run counter
             if auto_cnt /= 0 then
                 auto_cnt_next <= auto_cnt - 1;
             end if;
 
-            -- Automatic CS is set whenever state isn't IDLE or RECOVERY
-            if auto_state /= AUTO_IDLE and
-               auto_state /= AUTO_RECOVERY then
+            -- Automatic CS is set whenever state isn't IDLE or RECOVERY or BOOT
+            if  auto_state /= AUTO_IDLE and
+                auto_state /= AUTO_RECOVERY and
+                auto_state /= AUTO_BOOT then
                 auto_cs <= '1';
             end if;
 
             -- State machine
             case auto_state is
+            when AUTO_BOOT =>
+                if BOOT_CLOCKS then
+                    auto_cmd_valid <= '1';
+                    if cmd_ready = '1' then
+                        auto_next <= AUTO_IDLE;
+                    end if;
+                end if;
             when AUTO_IDLE =>
                 -- Access to the memory map only when manual CS isn't set
                 if wb_map_valid = '1' and ctrl_cs = '0' then
@@ -599,3 +610,4 @@ begin
     end process;
 
 end architecture;
+