Re: [Qemu-devel] [PATCH] tests: fix cdrom_pio_impl in ide-test

[John Snow <jsnow@redhat.com>]

On 11/20/2015 09:29 AM, Peter Lieven wrote:
> The check for the cleared BSY flag has to be performed
> before each data transfer and not just before the
> first one.
> 
> Commit 5f81724d revealed this glitch as the BSY flag
> was not set in ATAPI PIO transfers before.
> 
> While at it fix the desciptions and add a comment before

Descriptions, if this can be fixed on apply.

> the nested for loop that transfers the data.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  tests/ide-test.c |   16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/tests/ide-test.c b/tests/ide-test.c
> index d1014bb..fc1ce52 100644
> --- a/tests/ide-test.c
> +++ b/tests/ide-test.c
> @@ -699,24 +699,19 @@ static void cdrom_pio_impl(int nblocks)
>      outb(IDE_BASE + reg_lba_middle, BYTE_COUNT_LIMIT & 0xFF);
>      outb(IDE_BASE + reg_lba_high, (BYTE_COUNT_LIMIT >> 8 & 0xFF));
>      outb(IDE_BASE + reg_command, CMD_PACKET);
> -    /* HPD0: Check_Status_A State */
> +    /* HP0: Check_Status_A State */
>      nsleep(400);
>      data = ide_wait_clear(BSY);
> -    /* HPD1: Send_Packet State */
> +    /* HP1: Send_Packet State */
>      assert_bit_set(data, DRQ | DRDY);
>      assert_bit_clear(data, ERR | DF | BSY);
>  
>      /* SCSI CDB (READ10) -- read n*2048 bytes from block 0 */
>      send_scsi_cdb_read10(0, nblocks);
>  
> -    /* HPD3: INTRQ_Wait */
> +    /* HP3: INTRQ_Wait */
>      ide_wait_intr(IDE_PRIMARY_IRQ);
>  
> -    /* HPD2: Check_Status_B */
> -    data = ide_wait_clear(BSY);
> -    assert_bit_set(data, DRQ | DRDY);
> -    assert_bit_clear(data, ERR | DF | BSY);
> -
>      /* Read data back: occurs in bursts of 'BYTE_COUNT_LIMIT' bytes.
>       * If BYTE_COUNT_LIMIT is odd, we transfer BYTE_COUNT_LIMIT - 1 bytes.
>       * We allow an odd limit only when the remaining transfer size is
> @@ -728,6 +723,11 @@ static void cdrom_pio_impl(int nblocks)
>      for (i = 0; i < DIV_ROUND_UP(rxsize, limit); i++) {
>          size_t offset = i * (limit / 2);
>          size_t rem = (rxsize / 2) - offset;
> +        /* HP2: Check_Status_B */
> +        data = ide_wait_clear(BSY);
> +        assert_bit_set(data, DRQ | DRDY);
> +        assert_bit_clear(data, ERR | DF | BSY);
> +        /* HP4: Transfer_Data */
>          for (j = 0; j < MIN((limit / 2), rem); j++) {
>              rx[offset + j] = le16_to_cpu(inw(IDE_BASE + reg_data));
>          }
> 

This looks correct. This will definitely fix the race in the test, since
it was due to a race where we were reading the data when DRQ was not set.

Where I still remain a little confused is the precise flow control that
leads to sending an interrupt where BSY is set and DRQ is clear.

I'd like to investigate that a little more, but for purposes of rc1 and
testing I think this is the right thing to do.

For rc1, however:
Reviewed-by: John Snow <jsnow@redhat.com>