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Hi i'm studing how work ahci in detail. I have instrumented device
driver code libahci.c, in particular the <i>ahci_qc_issue</i>
function in that way:<br>
<br>
static unsigned int ahci_qc_issue(struct ata_queued_cmd *qc)<br>
{<br>
.<br>
.<br>
.<br>
if (qc->tf.protocol == ATA_PROT_NCQ){<br>
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);<br>
<br>
writel(1 << qc->tag, port_mmio + PORT_SCR_ACT);<br>
<br>
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);<br>
<br>
}<br>
.<br>
.<br>
.<br>
printk(KERN_DEBUG "ISSUE[before CI]: op1 = %lx, op2 =%08x, ci =
%08x, cmd = %02x\n", <br>
1<<qc->tag,
port_mmio+PORT_CMD_ISSUE,readl(port_mmio+PORT_CMD_ISSUE),qc->tf.command
& 0xff);<br>
writel(1 << qc->tag, port_mmio + PORT_CMD_ISSUE);<br>
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);<br>
.<br>
.<br>
.<br>
}<br>
<br>
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:<br>
<br>
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before SACT]: op1
= 1, op2 =f8408134, sact = 00000000, cmd = 61<br>
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before SACT]: op1
= 1, op2 =f8408134, sact = 00000001, cmd = 61<br>
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 =
1, op2 =f8408138, ci = 00000000, cmd = 61<br>
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 =
1, op2 =f8408138, ci = 00000000, cmd = 61<br>
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 =
1, op2 =f8408138, ci = 00000000, cmd = e7<br>
Jul 30 15:23:15 test kernel: [ 6673.022957] ISSUE[before CI]: op1 =
1, op2 =f8408138, ci = 00000001, cmd = e7<br>
<br>
We note that when driver issues a FPDMA WRITE (61) we observe the
anomaly.<br>
<br>
My question is: is there some simplification on device
implementation? Is there an explanation?<br>
<br>
Thanks for helping.<br>
<br>
Luigi<br>
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