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x86: qemu: add comment about qfw register endianness

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This patch adds some comments about qfw register endianness for clarity.

Signed-off-by: Miao Yan <yanmiaobest@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
This commit is contained in:
Miao Yan 2016-05-22 19:37:16 -07:00 committed by Bin Meng
parent 2e82e745a4
commit 331ba7db6c
1 changed files with 8 additions and 1 deletions
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9
arch/x86/cpu/qemu/qemu.c
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@ -17,6 +17,7 @@ static bool i440fx;
#ifdef CONFIG_QFW
/* on x86, the qfw registers are all IO ports */
#define FW_CONTROL_PORT 0x510
#define FW_DATA_PORT 0x511
#define FW_DMA_PORT_LOW 0x514
@ -31,15 +32,21 @@ static void qemu_x86_fwcfg_read_entry_pio(uint16_t entry,
/*
* writting FW_CFG_INVALID will cause read operation to resume at
* last offset, otherwise read will start at offset 0
*
* Note: on platform where the control register is IO port, the
* endianness is little endian.
*/
if (entry != FW_CFG_INVALID)
outw(entry, FW_CONTROL_PORT);
outw(cpu_to_le16(entry), FW_CONTROL_PORT);
/* the endianness of data register is string-preserving */
while (size--)
data[i++] = inb(FW_DATA_PORT);
}
static void qemu_x86_fwcfg_read_entry_dma(struct fw_cfg_dma_access *dma)
{
/* the DMA address register is big endian */
outl(cpu_to_be32((uint32_t)dma), FW_DMA_PORT_HIGH);
while (be32_to_cpu(dma->control) & ~FW_CFG_DMA_ERROR)