Re: [Draft Design v3] ACPI/IORT Support in Xen.

[Julien Grall <julien.grall@linaro.org>]

Hi Manish,

On 11/21/2017 07:22 AM, Manish Jaggi wrote:
> 
>   ACPI/IORT Support in Xen.
>   --------------------------
>        Draft 3
> 
>   Revision History:
> 
>   Changes since v2:
>   - Modified as per comments from Julien /Sameer/Andre
> 
>   Changes since v1:
>   - Modified IORT Parsing data structures.
>   - Added RID-StreamID and RID-DeviceID map as per Andre's suggestion.
>   - Added reference code which can be read along with this document.
>   - Removed domctl for DomU, it would be covered in PCI-PT design.
> 
>   Introduction:
>   -------------
> 
>   I had sent out patch series [0] to hide smmu from Dom0 IORT.
>   This document is a rework of the series as it:
>   (a) extends scope by adding parsing of IORT table once

Can you stick with one name. Either IORT or "IORT table" but not mixing 
both. Technically the T in IORT stands for Table. So it would be better 
if you only use "IORT" everywhere in that document.

>   and storing it in in-memory data structures, which can then be used
>   for querying. This would eliminate the need to parse complete iort

s/iort/IORT/

>   table multiple times.
> 
>   (b) Generation of IORT for domains be independent using a set of
>   helper routines.
> 
>   Index
>   --------
>   1. What is IORT. What are its components ?
>   2. Current Support in Xen
>   3. IORT for Dom0
>   4. IORT for DomU
>   5. Parsing of IORT in Xen
>   6. Generation of IORT
> 7. Implementation Phases
>   8. References
> 
>   1. IORT Structure ?
>   --------------------------------------------
>   IORT refers to Input Output remapping table. It is essentially used to 
> find
>   information about the IO topology (PCIRC-SMMU-ITS) and relationships 
> between
>   devices.
> 
>   A general structure of IORT [1]:
>   It has nodes for PCI RC, SMMU, ITS and Platform devices. Using an IORT 
> table
>   relationship between RID -> StreamID -> Deviceid can be obtained.
>   Which device is behind which SMMU and which interrupt controller, 
> topology
>   is described in IORT Table.
> 
>   Some PCI RC may be not behind an SMMU, and directly map RID-DeviceID.
> 
>   RID is a requester ID in PCI context,
>   StreamID is the ID of the device in SMMU context,
>   DeviceID is the ID programmed in ITS.
> 
>   Each iort_node contains an ID map array to translate one ID into another.
>   IDmap Entry {input_range, output_range, output_node_ref, id_count}
>   This array is associated with PCI RC node, SMMU node, Named component 
> node.
>   and can reference to a SMMU or ITS node.
> 
>   2. Support of IORT
>   ---------------------------
>   It is proposed in this document to parse iort once and use the 
> information
>   to translate RID without traversing IORT again and again.
> 
>   Also Xen prepares an IORT table for dom0 based on host IORT.
>   For DomU IORT table is required only in case of device passthrough.
> 
>   3. IORT for Dom0
>   -----------------
>   IORT for Dom0 is based on host iort. Few nodes could be removed or 
> modified.
>     For instance
>   - Host SMMU nodes should not be present as Xen should only touch it.
>   - platform devices (named components) would be passed as is. The 
> visibility
>     criterion for DOM0 is TDB.

s/TDB/TBD/

> 
>   4. IORT for DomU
>   -----------------
>   IORT for DomU should be generated by toolstack. IORT table is only 
> present
>   in case of device passthrough.
> 
>   At a minimum domU IORT should include a single PCIRC and ITS Group.

s/domU/DomU/

>   Similar PCIRC can be added in DSDT.
>   The exact structure of DomU IORT would be covered along with PCI PT 
> design.
> 
>   5. Parsing of IORT in Xen
>   --------------------------
>   IORT nodes can be saved in structures so that IORT table parsing can 
> be done
>   once and is reused by all xen subsystems like ITS / SMMU etc, domain 

s/xen/Xen/

> creation.
>   Proposed are the structures to hold IORT information. [4]
> 
>   struct rid_map_struct {
>      void *pcirc_node;
>      u16 inpute_base;
>      u32 output_base;
>      u16 id_ccount;

s/id_ccount/id_count/

>      struct list_head entry;
>   };
> 
> Two global variables would hold the maps.
>        struct list_head rid_streamid_map;
>        struct list_head rid_deviceid_map;
> 
>   5.1 Functions to query StreamID and DeviceID from RID.
> 
>   void query_streamid(void *pcirc_node, u16 rid, u32 *streamid);
>   void query_deviceid(void *pcirc_node, u16 rid, u32 *deviceid);

I don't fully understand what is the "void *pcirc_node" and how a caller 
would find it.

> 
>   Adding a mapping is done via helper functions
> 
>   int add_rid_streamid_map(void *pcirc_node, u32 ib, u32 ob, u32 idc)
>   int add_rid_deviceid_map(void *pcirc_node, u32 ib, u32 ob, u32 idc)

What does ib, ob, idc mean? I thought we asked to avoid unknown acronym.

>   - rid-streamid map is straight forward and is created using pci_rc's 
> idmap
>   - rid-deviceid map is created by translating streamids to deviceids.
>        fixup_rid_deviceid_map function does that. (See [6])

I will look at the code when it is formally sent on the mailing list. 
The design documents looks good, thought it may need to be refine during 
the code review.

> 
> To keep the api similar to linux iort_node_map_rid be mapped to
> query_streamid
> 
> 6. IORT Generation
> -------------------
> It is proposed to have a common helper library to generate IORT for dom0/U.
> Note: it is desired to have IORT generation code sharing between toolstack
> and Xen.
> 
> a. For Dom0
>   rid_deviceId_map can be used directly to generate dom0 IORT table.
>   Exclusions of nodes is still open for suggestions.
> 
> b. For DomU
>   Minimal structure is discussed in section 4. It will be further discussed
>   in the context of PCI PT design.
> 
> 7. Implementation Phases
> -------------------------
> a. IORT Parsing and RID Query
> b. IORT Generation for Dom0
> c. IORT Generation for DomU.
> 
> 8. References:
> -------------
> [0] https://www.mail-archive.com/xen-devel@lists.xen.org/msg121667.html
> [1] ARM DEN0049C: 
> http://infocenter.arm.com/help/topic/com.arm.doc.den0049c/DEN0049C_IO_Remapping_Table.pdf 
> 
> [2] https://www.mail-archive.com/xen-devel@lists.xen.org/msg123082.html
> [3] NA.
> [4] https://www.mail-archive.com/xen-devel@lists.xen.org/msg123434.html
> [5] https://www.mail-archive.com/xen-devel@lists.xen.org/msg123080.html
> [6] 
> https://github.com/mjaggi-cavium/xen-wip/commit/df006d64bdbb5c8344de5a710da8bf64c9e8edd5 

Cheers,

-- 
Julien Grall

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