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

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Message-ID: <cfaf2fbb-5c6a-9f85-fdc9-325d82fb7821@loongson.cn>
Date: Wed, 28 May 2025 17:34:49 +0800
From: Qunqin Zhao <zhaoqunqin@...ngson.cn>
To: Stefano Garzarella <sgarzare@...hat.com>
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


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.

Thanks,

Qunqin

>
> And TPM_CHIP_FLAG_IRQ flag can remind us this hardware is "IRQ" not 
> "POLL".
>
> Thanks,
>
> Qunqin.
>
>>
>> Thanks,
>> Stefano