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

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Message-ID: <7a0c5eae-f6c7-f2dc-9356-5419c7df4f6a@loongson.cn>
Date: Thu, 29 May 2025 10:16:05 +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5:53, Stefano Garzarella 写道:
> 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.

I need to copy the data to the DMA data buffer. So my suggestion is to 
let the vendor specific driver  decide whether to use the SYNC or IRQ flag.

IRQ flag is fine for me.

Thanks,

Qunqin.

>
> Stefano