[spi_device] 2nd part of the Technical Specification #9974

eunchan · 2022-01-10T21:56:03Z

This PR adds the remained flash mode and passthrough mode on top of #9951 .

kosta-kojdic · 2022-01-11T09:52:24Z

hw/ip/spi_device/doc/_index.md

+Details of the fields are explained in the {{<regref "CMD_INFO_0">}}
+
+First 11 commands are assigned to specific submodules.
+


Can you document required encodings for the first 11 commands? As of now all reset values are 0, so it is important to have proper commands configured in the first 11 slots.

OK. Since I don't see any reason to have other than the fixed value for Read Status, Read JEDEC ID, and Read SFDP, I may follow the same process as EN4B / EX4B, which means, SW just configure valid and opcode.

I will create an issue and follow up.

tjaychen · 2022-01-11T19:50:43Z

hw/ip/spi_device/doc/_index.md

+
+- Support Serial Flash emulation
+  - HW processed Read Status, Read JEDEC ID, Read SFDP, EN4B/ EX4B, and multiple read commands
+  - 16 depth Command/ Address FIFOs and Payload buffer for command upload


could you mention the payload buffer size?

tjaychen · 2022-01-11T19:51:51Z

hw/ip/spi_device/doc/_index.md

@@ -49,6 +69,38 @@ The SW can receive TPM commands with payload (address and data) and respond to t
 The submodule provides the command, address, write, and read FIFOs for the SW to communicate with the TPM host system.
 The submodule also supports the SW by managing a certain set of the FIFO registers and returning the read request by HW quickly.

+In Flash mode, SPI Device HWIP behaves as a Serial Flash device by recognizing SPI Flash commands and processing those commands by HW.
+The commands processed by HW are Read Status (1, 2, 3), Read JEDEC ID, Read SFDP, EN4B/ EX4B, and read commands with aids of SW.


aids -> aid

tjaychen · 2022-01-11T19:52:32Z

hw/ip/spi_device/doc/_index.md

+
+In Passthrough mode, SPI Device receives SPI transactions from a host system and forwards the transactions to a downstream flash device.
+SW may filter prohibited commands by configuring 256-bit {{< regref "FILTER" >}} CSR.
+The IP cancels ongoing transaction if the received opcode matches to the filter CSR by de-asserting CSb and gating SCK  to the downstream flash device.


extra space after SCK

Blame my keyboard. It easily adds additional space ... I probably switch the switch .

tjaychen · 2022-01-11T19:52:59Z

hw/ip/spi_device/doc/_index.md

+
+SW may program CSRs to change the address and/or the first 4 bytes of payload on-the-fly in Passthrough mode.
+The address translation feature allows SW to maintain A/B binary images without aids of the host system.
+The payload translation may be used to change the payload of Write Status commands to not allow certain fiels to be modified.


fiels -> fields

Another blame to my kb 😀

tjaychen · 2022-01-11T19:53:26Z

hw/ip/spi_device/doc/_index.md

+The address translation feature allows SW to maintain A/B binary images without aids of the host system.
+The payload translation may be used to change the payload of Write Status commands to not allow certain fiels to be modified.
+
+Flash mode and Passthrough mode may share the datapath.


i think instead of saying "share the datapath", i feel like "active at the same time" might be clearer.

I agree that is clearer. However, the mode register can't be active both. Flash mode or Passthrough. In passthrough, flash mode can be active. That is intention. Let me rephrase the sentence.

tjaychen · 2022-01-11T19:54:56Z

hw/ip/spi_device/doc/_index.md

+Generic mode is exclusive. Flash and Passthrough modes share many parts of the datapath.
+TPM mode only shares the SPI and has separate CSb port, which allows that the host sends TPM commands while other SPI mode is active.
+
+Mod      | FwMode | Status | JEDEC | SFDP | Mailbox | Read | Addr4B | Upload | Passthrough


does the passthrough / passthru intercept box need a Y?

Thanks! @msfschaffner also pointed out. Revised.

tjaychen · 2022-01-11T20:23:38Z

hw/ip/spi_device/doc/_index.md

+[4]    | Read SFDP
+[10:5] | Read commands
+
+When Read Status, Read JEDEC ID commands are processed in Flash mode, the other fields in the command information entry are not used.


just to make sure i understand, if we are in flash mode, OR we are in passthrough mode with intercept_en set, the other fields of these configurations are ignored right? If what i'm saying is true, it may be clearer to describe it that way.

Right. Thanks for pointing it out.

tjaychen · 2022-01-11T20:26:11Z

hw/ip/spi_device/doc/_index.md

+As explained in the [previous section](#command-information-list), the command parser checks the index to activate Read Status / Read JEDEC ID/ Read Command / Address 4B modules.
+Other than the first 11 slots and last two slots (the last two slots are not visible to SW), the cmdparse checks the *upload* field and activates the upload module if the field is set.
+
+SW may configure the submodules if the modules process the command in the passthrough mode or not by changing {{<regref "INTERCEPT_EN">}} CSR.


just to double check, you are saying that the submodules will process the command in passthrough mode only if the intercept_en is set right?

Yes. Revised the sentence.

tjaychen · 2022-01-11T20:27:18Z

hw/ip/spi_device/doc/_index.md

+
+### Status Control
+
+If the received command is one of the three read status commands, STATUS control module reigns SPI interface after the opcode.


reigns? just to be sure, you mean the status control module will take over the spi interface right?

Yep. "take over" is way better 👍

tjaychen · 2022-01-11T20:31:04Z

hw/ip/spi_device/doc/_index.md

+When the module receives `addr[0]`, at the positive edge of SCK, the module moves to appropriate command state based on the given CMD_INFO data.
+
+If the received address falls into mailbox address ragne and mailbox feature is enabled, the module turns on the mailbox selection bit.
+Then all out-going requests to the DPSRAM are forwarded to the mailbox section, not the read buffer section.


just wanted to clarify one thing here. If the mailbox space is for example located ahead of other space, we DO NOT dynamically switch right? Ie, once you start in mailbox, even if you read into non-mailbox space, will we still remain in mailbox space?

I'm not suggesting we change anything, just that it would be good to clarify the behavior.

Hum... good point. Let me check the design. I am honestly not sure about the behavior.

tjaychen · 2022-01-11T21:01:49Z

hw/ip/spi_device/doc/_index.md

+Also the HW updates {{<regref "CFG.addr_4b_en">}} after passing through CDC.
+It takes at most three SYS_CLK cycles to update the value in the *CFG* register after the completion of the SPI transaction (CSb de-assertion).
+
+_Note: The HW changes the broadcasting signal and the CSR even thought eh SPI host system sends more than 8 beats of the SPI S[0].


nit, extra underscore in front of Note? or maybe that was intended.

even thought -> even though

tjaychen

some nitpicks, but overall this looks great to me.

msfschaffner

LGTM with a few nits

msfschaffner · 2022-01-12T00:58:19Z

hw/ip/spi_device/doc/_index.md

+As explained in the [previous section](#command-information-list), the command parser checks the index to activate Read Status / Read JEDEC ID/ Read Command / Address 4B modules.
+Other than the first 11 slots and last two slots (the last two slots are not visible to SW), the cmdparse checks the *upload* field and activates the upload module if the field is set.
+
+SW can configure whether a submodule shoudl process the command while in the passthrough mode by setting the {{<regref "INTERCEPT_EN">}} CSR.


nit: shoudl -> should

msfschaffner · 2022-01-12T01:01:15Z

hw/ip/spi_device/doc/_index.md

+Also the HW updates {{<regref "CFG.addr_4b_en">}} after passing through CDC.
+It takes at most three SYS_CLK cycles to update the value in the *CFG* register after the completion of the SPI transaction (CSb de-assertion).
+
+_Note: The HW changes the broadcasting signal and the CSR even though eh SPI host system sends more than 8 beats of the SPI S[0].


nit: eh -> the

msfschaffner · 2022-01-12T01:01:33Z

hw/ip/spi_device/doc/_index.md

+_Note: The HW changes the broadcasting signal and the CSR even though eh SPI host system sends more than 8 beats of the SPI S[0].
+After the logic matches the received command byte with EN4B/ EX4B, the logic ignores the rest of the SPI data._
+
+The broadcasted `cfg_addr_4b_en` signal affects the read commands which `addr_mode` is *AddrCfg* in their command informatio entries.


nit: informatio -> information

msfschaffner · 2022-01-12T01:02:10Z

hw/ip/spi_device/doc/_index.md

+- The command matches to any of the rest command information entries.
+- The matched entry has the `upload` field set.
+
+The upload module checks  the command information entry to determine whether the address/ payload fields to be uploaded or not.


nit: two spaces

msfschaffner · 2022-01-12T01:04:32Z

hw/ip/spi_device/doc/_index.md

+The information of the pad enable and direction is given by SW.
+SW configures the address size, payload lanes, dummy size in **CMD_INFO** slots.
+
+If passthrough logic does not find valid commandinformation entry based on the received opcode, it assumes the command is **PayloadIn&** Single IO command.


nit: commandinformation -> command information

also, is the & intended in **PayloadIn&**?

eunchan · 2022-01-12T18:38:54Z

I don't think this PR affects ROM binary and FPGA tests. Let me merge this.

This commit adds the flash and passthrough modes in the technical specification. Signed-off-by: Eunchan Kim <[email protected]>

eunchan requested review from tjaychen, weicaiyang and kosta-kojdic January 10, 2022 21:56

eunchan force-pushed the spi_doc2 branch from 8a07407 to 92130d7 Compare January 10, 2022 21:56

kosta-kojdic reviewed Jan 11, 2022

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eunchan force-pushed the spi_doc2 branch from 92130d7 to 7fef8e7 Compare January 11, 2022 23:25

This was referenced Jan 11, 2022

[spi_device] Technical Specification #9951

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[spi_device] HW to not cross the mailbox space #10008

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eunchan force-pushed the spi_doc2 branch from 7fef8e7 to de74463 Compare January 11, 2022 23:46

eunchan mentioned this pull request Jan 11, 2022

[spi_device] Read Status, Read JEDEC ID, Read SFDP to have fixed value (read-only) in CMD_INFO #10009

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eunchan force-pushed the spi_doc2 branch from de74463 to bf21f7c Compare January 12, 2022 01:35

[spi_device] Technical Specification

be2aec9

This commit adds the flash and passthrough modes in the technical specification. Signed-off-by: Eunchan Kim <[email protected]>

eunchan force-pushed the spi_doc2 branch from bf21f7c to be2aec9 Compare January 12, 2022 18:39

eunchan merged commit be2aec9 into lowRISC:master Jan 12, 2022

eunchan deleted the spi_doc2 branch January 12, 2022 18:39

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[spi_device] 2nd part of the Technical Specification #9974

[spi_device] 2nd part of the Technical Specification #9974

eunchan commented Jan 10, 2022

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eunchan commented Jan 12, 2022

		Details of the fields are explained in the {{<regref "CMD_INFO_0">}}

		First 11 commands are assigned to specific submodules.


		### Status Control

		If the received command is one of the three read status commands, STATUS control module reigns SPI interface after the opcode.

[spi_device] 2nd part of the Technical Specification #9974

[spi_device] 2nd part of the Technical Specification #9974

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eunchan commented Jan 10, 2022

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eunchan commented Jan 12, 2022

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