Hi i'm studing how work ahci in detail. I have instrumented device
driver code libahci.c, in particular the /ahci_qc_issue/ function in
that way:
static unsigned int ahci_qc_issue(struct ata_queued_cmd *qc)
{
.
.
.
if (qc->tf.protocol == ATA_PROT_NCQ){
printk(KERN_DEBUG "ISSUE[before SACT]: op1 = %lx, op2 =%08x,
sact = %08x, cmd = %02x\n", 1<<qc->tag,
port_mmio+PORT_SCR_ACT,readl(port_mmio+PORT_SCR_ACT),qc->tf.command & 0xff);
writel(1 << qc->tag, port_mmio + PORT_SCR_ACT);
printk(KERN_DEBUG "ISSUE[before SACT]: op1 = %lx, op2 =%08x,
sact = %08x, cmd = %02x\n", 1<<qc->tag,
port_mmio+PORT_SCR_ACT,readl(port_mmio+PORT_SCR_ACT),qc->tf.command & 0xff);
}
.
.
.
printk(KERN_DEBUG "ISSUE[before CI]: op1 = %lx, op2 =%08x, ci = %08x,
cmd = %02x\n",
1<<qc->tag,
port_mmio+PORT_CMD_ISSUE,readl(port_mmio+PORT_CMD_ISSUE),qc->tf.command
& 0xff);
writel(1 << qc->tag, port_mmio + PORT_CMD_ISSUE);
printk(KERN_DEBUG "ISSUE[before CI]: op1 = %lx, op2 =%08x, ci =
%08x, cmd = %02x\n", 1<<qc->tag,
port_mmio+PORT_CMD_ISSUE,readl(port_mmio+PORT_CMD_ISSUE),qc->tf.command
& 0xff);
.
.
.
}
When running driver i observe strange behavior: when driver issues a NCQ
command, SACT register is written with proper value, while CI register
not. Why? Instead, when driver issues a NON-NCQ command CI register is
written with proper value. To better explain i show a piece of log:
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before SACT]: op1 = 1,
op2 =f8408134, sact = 00000000, cmd = 61
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before SACT]: op1 = 1,
op2 =f8408134, sact = 00000001, cmd = 61
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 = 1,
op2 =f8408138, ci = 00000000, cmd = 61
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 = 1,
op2 =f8408138, ci = 00000000, cmd = 61
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 = 1,
op2 =f8408138, ci = 00000000, cmd = e7
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 = 1,
op2 =f8408138, ci = 00000001, cmd = e7
We note that when driver issues a FPDMA WRITE (61) we observe the anomaly.
My question is: is there some simplification on device implementation?
Is there an explanation?
Thanks for helping.
Luigi
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