[U-Boot] [EXT] Re: [PATCH 7/7] scsi: dts: a3700: add scsi node

[Simon Glass]

Hi Ken,

On 27 March 2017 at 02:28, Ken Ma <make at marvell.com> wrote:
> Hi Stefan
>
>
>
> Thanks a lot for your kind reply.
>
>
>
> But I still do not think it's very good to change sata's uclass id from
> "UCLASS_AHCI" to "UCLASS_SCSI".
>
> If we do such change, UCLASS_AHCI is lost since from the sata.c codes, it
> does the AHCI initialization work but not SCSI initialization work.
>
> If u-boot supports ISIS scanner which supports SCSI, I think its uclass id
> should be like UCLASS_ISIS but not UCLASS_SCSI.
>
> And if we set sata's uclass id as "UCLASS_SCSI", it should provide basic
> SCSI function, then why can’t we connect a parallel SCSI device like SCSI
> scanner or cd-rom to the SATA interface?
>
> From https://en.wikipedia.org/wiki/Serial_ATA#SATA_and_SCSI
>
> In general, SATA devices link compatibly to SAS enclosures and adapters,
> whereas SCSI devices cannot be directly connected to a SATA bus
>
>
>
>
>
> Actually Marvell’s sata controller is SAS(Serial Attached SCSI system), it
> integrates SCSI and SATA(AHCI); SAS provides a SCSI bus which works only in
> SAS range(for example, 2 sata ports in SAS), so actually the SCSI bus
> controller is not "virtual" controllers but has the same device base
> register as SATA.
>
>
>
> From https://en.wikipedia.org/wiki/Serial_Attached_SCSI
>
> A typical Serial Attached SCSI system consists of the following basic
> components:
>
> 1.    An initiator: a device that originates device-service and
> task-management requests for processing by a target device and receives
> responses for the same requests from other target devices. Initiators may be
> provided as an on-board component on the motherboard (as is the case with
> many server-oriented motherboards) or as an add-on host bus adapter.
>
> 2.    A target: …
>
> So in my opinion, there are two ways to implement SAS as below
>
> A.  If our codes provide SAS controller as an on-board component – then a
> uclass id of UCLASS_SAS should be defined and then in scsi_scan() of
> scsi_scan.c, both devices of UCLASS_SCSI and UCLASS_SAS should be scanned.
> In such implementation, UCLASS_SCSI is for parallel SCSI while UCLASS_SAS is
> for serial attached SCSI;
>
> B.  SAS works as an add-on host bus adapter as above said, SAS’s SCSI
> controller and AHCI controller are both itself as below - SCSI controller is
> not a virtual device, it exists and only works in SAS internal range(since
> there is no UCLASS_SAS, I take this way);
>
> Although the SAS’s SCSI controller does not need to any special hardware
> configuration; but actually I think there is something to do, we should bind
> special scsi_exec() to SCSI devices in SCSI driver or SAS driver (For
> different SCSI controls, SAS must have different implementation of
> scsi_exec() comparing to SCSI scanner, or other SCSI devices)
>
> By the way, I think we should move the work of creating block devices to
> scsi-uclass.c
>
> scsi: scsi at e0000 {
>
>                         compatible = "marvell,mvebu-scsi";
>
> reg = <0xe0000 0x2000>;
>
>                         sata: sata at e0000 {
>
>                               compatible = "marvell,armada-3700-ahci";
>
>                               reg = <0xe0000 0x2000>;
>
>                               interrupts = <GIC_SPI 27 IRQ_TYPE_LEVEL_HIGH>;
>
>                         };

Does this match the Linux DT?
>
>                   };
>
>
>
>
>
> Yours,
>
> Ken

Regards,
Simon