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hw/arm/strongarm: Fix handling of GPSR/GPCR reads 

The StrongARM GPIO GPSR and GPCR registers are write-only, with reads being
undefined behaviour. Instead of having GPCR return 31337 and GPSR return
the value last written, make both log the guest error and return 0.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
This commit is contained in:
Peter Maydell 2014-06-29 18:38:39 +01:00
parent 6e411af935
commit 92335a0d40
1 changed files with 6 additions and 8 deletions
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14
hw/arm/strongarm.c
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@ -480,7 +480,6 @@ struct StrongARMGPIOInfo {
uint32_t rising;
uint32_t falling;
uint32_t status;
uint32_t gpsr;
uint32_t gafr;
uint32_t prev_level;
@ -544,14 +543,14 @@ static uint64_t strongarm_gpio_read(void *opaque, hwaddr offset,
return s->dir;
case GPSR: /* GPIO Pin-Output Set registers */
DPRINTF("%s: Read from a write-only register 0x" TARGET_FMT_plx "\n",
__func__, offset);
return s->gpsr; /* Return last written value. */
qemu_log_mask(LOG_GUEST_ERROR,
"strongarm GPIO: read from write only register GPSR\n");
return 0;
case GPCR: /* GPIO Pin-Output Clear registers */
DPRINTF("%s: Read from a write-only register 0x" TARGET_FMT_plx "\n",
__func__, offset);
return 31337; /* Specified as unpredictable in the docs. */
qemu_log_mask(LOG_GUEST_ERROR,
"strongarm GPIO: read from write only register GPCR\n");
return 0;
case GRER: /* GPIO Rising-Edge Detect Enable registers */
return s->rising;
@ -590,7 +589,6 @@ static void strongarm_gpio_write(void *opaque, hwaddr offset,
case GPSR: /* GPIO Pin-Output Set registers */
s->olevel |= value;
strongarm_gpio_handler_update(s);
s->gpsr = value;
break;
case GPCR: /* GPIO Pin-Output Clear registers */