Hi Ken,
On 05.04.2017 11:29, Ken Ma wrote:
Hi Stefan, Hi Simon
Please see my inline reply, thanks!
Yours, Ken
-----Original Message----- From: Stefan Roese [mailto:sr@denx.de] Sent: 2017年4月3日 14:14 To: Simon Glass; Ken Ma Cc: u-boot@lists.denx.de; Michal Simek; Kostya Porotchkin; Hua Jing; Wilson Ding Subject: Re: [EXT] Re: [PATCH 7/7] scsi: dts: a3700: add scsi node
Hi Simon, Hi Ken,
On 01.04.2017 06:22, Simon Glass wrote:
On 27 March 2017 at 02:28, Ken Ma make@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:
- 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.
- 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@e0000 {
compatible = "marvell,mvebu-scsi";reg = <0xe0000 0x2000>;
sata: sata@e0000 { compatible ="marvell,armada-3700-ahci";
reg = <0xe0000 0x2000>; interrupts = <GIC_SPI 27IRQ_TYPE_LEVEL_HIGH>;
};Does this match the Linux DT?
No, and this is my main concern. This patch series introduces a new "scsi" DT node and moves the controller(s) one level up into this newly created DT node (Ken please correct me if I'm wrong here). We simply can't make such changes here in U-Boot without this being first discussed and decided on the Linux DT mailing list with the DT maintainers.
Ken, how is this problem solved / handled in Linux without this DT changes up until now?
[Ken] Actually I do not find any SCSI nodes/compatible strings In Linux; if aligned to linux, then we should have no scsi nodes at all in u-boot.
Thats exactly what I meant. The DT represents the hardware and only controllers / devices etc are listed here. As such, only the SATA, AHCI, IDE (etc.) controllers are listed behind their internal SoC / CPU busses in the DT. Unfortunately we can't come up with this new SCSI DT node for U-Boot and move all the controllers into this node, as we need to try to stay in sync with the Linux DT, which is the reference.
I am not familiar with Linux SCSI implementation, it seems that SCSI bus is implemented as a middle layer in Linux since it has no SCSI fdt nodes.
Frankly, I've not looked at SCSI in Linux for quite some time. So I can't really tell you how this is handled there. But I'm pretty sure that no SCSI DT nodes / properties are involved here.
Thanks, Stefan