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

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Message-ID: <gymx5tbghi55gm76ydtuzzd6r522expft36twwtvpkbgcl266a@zelnthnhu7kq>
Date: Wed, 28 May 2025 11:00:12 +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 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.

Thanks,
Stefano