linux-kernel - Re: [PATCH v10 4/5] tpm: Add a driver for Loongson TPM device

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <45xqguhrecn57cwc66hfws4eeqrb6rlijvh2z35e56ogojc2q4@pnlrgx57353b>
Date: Wed, 28 May 2025 11:53:16 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Qunqin Zhao <zhaoqunqin@...ngson.cn>
Cc: lee@...nel.org, herbert@...dor.apana.org.au, jarkko@...nel.org, 
	linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev, davem@...emloft.net, 
	linux-crypto@...r.kernel.org, peterhuewe@....de, jgg@...pe.ca, linux-integrity@...r.kernel.org, 
	Yinggang Gu <guyinggang@...ngson.cn>, Huacai Chen <chenhuacai@...ngson.cn>
Subject: Re: [PATCH v10 4/5] tpm: Add a driver for Loongson TPM device

On Wed, May 28, 2025 at 05:34:49PM +0800, Qunqin Zhao wrote:
>
>在 2025/5/28 下午5:24, Qunqin Zhao 写道:
>>
>>在 2025/5/28 下午5:00, Stefano Garzarella 写道:
>>>On Wed, May 28, 2025 at 04:42:05PM +0800, Qunqin Zhao wrote:
>>>>
>>>>在 2025/5/28 下午3:57, Stefano Garzarella 写道:
>>>>>>+    chip = tpmm_chip_alloc(dev, &tpm_loongson_ops);
>>>>>>+    if (IS_ERR(chip))
>>>>>>+        return PTR_ERR(chip);
>>>>>>+    chip->flags = TPM_CHIP_FLAG_TPM2 | TPM_CHIP_FLAG_IRQ;
>>>>>
>>>>>Why setting TPM_CHIP_FLAG_IRQ?
>>>>
>>>>When tpm_engine completes  TPM_CC* command,
>>>>
>>>>the hardware will indeed trigger an interrupt to the kernel.
>>>
>>>IIUC that is hidden by loongson_se_send_engine_cmd(), that for 
>>>this driver is completely synchronous, no?
>>>
>>>>
>>>>>
>>>>>IIUC this driver is similar to ftpm and svsm where the send is 
>>>>>synchronous so having .status, .cancel, etc. set to 0 should 
>>>>>be enough to call .recv() just after send() in 
>>>>>tpm_try_transmit(). See commit 980a573621ea ("tpm: Make 
>>>>>chip->{status,cancel,req_canceled} opt")
>>>>The send callback would wait until the TPM_CC* command complete. 
>>>>We don't need a poll.
>>>
>>>Right, that's what I was saying too, send() is synchronous (as in 
>>>ftpm and svsm). The polling in tpm_try_transmit() is already 
>>>skipped since we are setting .status = 0, .req_complete_mask = 0, 
>>>.req_complete_val = 0, etc. so IMHO this is exactly the same of 
>>>ftpm and svsm, so we don't need to set TPM_CHIP_FLAG_IRQ.
>>
>>I see,  but why not skip polling directly in "if (chip->flags & 
>>TPM_CHIP_FLAG_IRQ)"  instead of do while?
>
>I mean, why not skip polling directly in "if (chip->flags & 
>TPM_CHIP_FLAG_IRQ)"?
>
>And In my opinion, TPM_CHIP_FLAG_SYNC and TPM_CHIP_FLAG_IRQ are 
>essentially the same, only with different names.

When TPM_CHIP_FLAG_SYNC is defined, the .recv() is not invoked and 
.send() will send the command and retrieve the response. For some driver 
like ftpm this will save an extra copy/buffer.

Stefano