NVMe driver init sequence

[Warner Losh]

This sounds right to me....  Most BIOSes seem to enable BME=1.

Warner

On Thu, Aug 17, 2017 at 2:45 PM, Kinjal Patel <Kinjal.Patel at taec.toshiba.com
> wrote:

> Hi,
>
> I have a query on NVMe driver init sequence in FreeBSD 10.3(stable).
>
> The driver init sequence is,
>
> 1)      Enable controller (CC.EN=1)
>
> 2)      Wait for controller ready (CSTS.RDY=1)
>
> 3)      Set PCI bus master enable (BME=1)
>
> As per NVMe spec, when NVMe controller becomes ready it has to process
> command.
>
> "Enable (EN): When set to '1', then the controller shall process commands
> based on Submission Queue Tail doorbell writes"
>
> And per PCI Express spec when BME is not set, the PCI Express Function is
> not allowed to issue any Memory or I/O requests.
> "Bus Master Enable - Controls the ability of a PCI Express Endpoint to
> issue Memory95 and I/O Read/Write Requests, and
> the ability of a Root or Switch Port to forward Memory and I/O Read/Write
> Requests in the Upstream direction"
>
> Enabling controller before setting BME=1 is violation of spec, as
> controller has to accept commands but BME is prerequisite for that.
>
> The Linux device driver init sequence is,
>
> 1)     Set PCI bus master enable (BME=1)
>
> 2)     Enable Controller (CC.EN=1)
>
> 3)     Wait for controller ready (CSTS.RDY=1)
>
> The FreeBSD NVMe driver sequence should be changed to set BME=1 before
> attempting to enable controller.
>
>
> Regards,
> Kinjal Patel
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