aspeed/smc: Inject errors in DMA checksum

Emulate read errors in the DMA Checksum Register for high frequencies
and optimistic settings of the Read Timing Compensation Register. This
will help in tuning the SPI timing calibration algorithm. Errors are
only injected when the property "inject_failure" is set to true as
suggested by Philippe.

The values below are those to expect from the first flash device of
the FMC controller of a palmetto-bmc machine.

Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NCédric Le Goater <clg@kaod.org>
Reviewed-by: NJoel Stanley <joel@jms.id.au>
Message-id: 20190904070506.1052-8-clg@kaod.org
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/ssi/aspeed_smc.c

@@ -869,6 +869,36 @@ static void aspeed_smc_dma_calibration(AspeedSMCState *s)
     s->regs[s->r_ctrl0 + cs] |= CE_CTRL_CLOCK_FREQ(hclk_div);
 }
 
+/*
+ * Emulate read errors in the DMA Checksum Register for high
+ * frequencies and optimistic settings of the Read Timing Compensation
+ * Register. This will help in tuning the SPI timing calibration
+ * algorithm.
+ */
+static bool aspeed_smc_inject_read_failure(AspeedSMCState *s)
+{
+    uint8_t delay =
+        (s->regs[R_DMA_CTRL] >> DMA_CTRL_DELAY_SHIFT) & DMA_CTRL_DELAY_MASK;
+    uint8_t hclk_mask =
+        (s->regs[R_DMA_CTRL] >> DMA_CTRL_FREQ_SHIFT) & DMA_CTRL_FREQ_MASK;
+
+    /*
+     * Typical values of a palmetto-bmc machine.
+     */
+    switch (aspeed_smc_hclk_divisor(hclk_mask)) {
+    case 4 ... 16:
+        return false;
+    case 3: /* at least one HCLK cycle delay */
+        return (delay & 0x7) < 1;
+    case 2: /* at least two HCLK cycle delay */
+        return (delay & 0x7) < 2;
+    case 1: /* (> 100MHz) is above the max freq of the controller */
+        return true;
+    default:
+        g_assert_not_reached();
+    }
+}
+
 /*
  * Accumulate the result of the reads to provide a checksum that will
  * be used to validate the read timing settings.
@@ -905,6 +935,11 @@ static void aspeed_smc_dma_checksum(AspeedSMCState *s)
         s->regs[R_DMA_FLASH_ADDR] += 4;
         s->regs[R_DMA_LEN] -= 4;
     }
+
+    if (s->inject_failure && aspeed_smc_inject_read_failure(s)) {
+        s->regs[R_DMA_CHECKSUM] = 0xbadc0de;
+    }
+
 }
 
 static void aspeed_smc_dma_rw(AspeedSMCState *s)
@@ -1185,6 +1220,7 @@ static const VMStateDescription vmstate_aspeed_smc = {
 
 static Property aspeed_smc_properties[] = {
     DEFINE_PROP_UINT32("num-cs", AspeedSMCState, num_cs, 1),
+    DEFINE_PROP_BOOL("inject-failure", AspeedSMCState, inject_failure, false),
     DEFINE_PROP_UINT64("sdram-base", AspeedSMCState, sdram_base, 0),
     DEFINE_PROP_LINK("dram", AspeedSMCState, dram_mr,
                      TYPE_MEMORY_REGION, MemoryRegion *),

include/hw/ssi/aspeed_smc.h

@@ -88,6 +88,7 @@ typedef struct AspeedSMCState {
 
     uint32_t num_cs;
     qemu_irq *cs_lines;
+    bool inject_failure;
 
     SSIBus *spi;