[RFC PATCH 2/2] hw/sd: skip double power-up in sd_vmstate_pre_load()

[Daniel Henrique Barboza <dbarboza@ventanamicro.com>]

At this moment any migration with the RISC-V sifive_u machine
fails with the following error:

qemu-system-riscv64: ../hw/sd/sd.c:297: sd_ocr_powerup: Assertion
`!FIELD_EX32(sd->ocr, OCR, CARD_POWER_UP)' failed.

The assert was introduced by dd26eb43337a ("hw/sd: model a power-up
delay, as a workaround for an EDK2 bug"). It introduced a delayed timer
of 0.5ms to power up the card after the first ACMD41 command. The assert
prevents the card from being turned on twice.

When migrating a machine that uses a sd card, e.g. RISC-V sifive_u, the
card is turned on during machine_init() in both source and destination
hosts. When the migration stream finishes in the destination, the
pre_load() hook will attempt to turn on the card before loading its
vmstate. The assert() is always going to hit because the card was
already on.

Change sd_vmstate_pre_load() to check first if the sd card is turned on
before executing a sd_ocr_powerup() and triggering the assert.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 hw/sd/sd.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/hw/sd/sd.c b/hw/sd/sd.c
index bd88c1a8f0..4add719643 100644
--- a/hw/sd/sd.c
+++ b/hw/sd/sd.c
@@ -664,11 +664,19 @@ static int sd_vmstate_pre_load(void *opaque)
 {
     SDState *sd = opaque;
 
-    /* If the OCR state is not included (prior versions, or not
+    /*
+     * If the OCR state is not included (prior versions, or not
      * needed), then the OCR must be set as powered up. If the OCR state
      * is included, this will be replaced by the state restore.
+     *
+     * However, there's a chance that the board will powerup the SD
+     * before reaching INMIGRATE state in the destination host.
+     * Powering up the SD again in this case will cause an assert
+     * inside sd_ocr_powerup(). Skip sd_ocr_powerup() in this case.
      */
-    sd_ocr_powerup(sd);
+    if (!sd_card_powered_up(sd)) {
+        sd_ocr_powerup(sd);
+    }
 
     return 0;
 }
-- 
2.39.0