linux-kernel - Re: [PATCH v6 4/4] x86/sev: register tpm-svsm platform device

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Message-ID: <eqtiiphs6rtjo7nirkw7zcicew75wnl4ydenrt5vl6jdpqdgj6@2brjlyjbqhoq>
Date: Tue, 8 Apr 2025 13:08:36 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Jarkko Sakkinen <jarkko@...nel.org>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>, 
	"H. Peter Anvin" <hpa@...or.com>, linux-coco@...ts.linux.dev, linux-integrity@...r.kernel.org, 
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org, Tom Lendacky <thomas.lendacky@....com>, 
	Joerg Roedel <jroedel@...e.de>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Claudio Carvalho <cclaudio@...ux.ibm.com>, James Bottomley <James.Bottomley@...senpartnership.com>, 
	linux-kernel@...r.kernel.org, Dov Murik <dovmurik@...ux.ibm.com>, 
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 4/4] x86/sev: register tpm-svsm platform device

On Tue, Apr 08, 2025 at 01:00:12PM +0200, Borislav Petkov wrote:
>On Thu, Apr 03, 2025 at 12:09:42PM +0200, Stefano Garzarella wrote:
>> @@ -2697,6 +2702,9 @@ static int __init snp_init_platform_device(void)
>>  	if (platform_device_register(&sev_guest_device))
>>  		return -ENODEV;
>>
>> +	if (platform_device_register(&tpm_svsm_device))
>> +		return -ENODEV;
>
>So I don't understand the design here:
>
>You've exported the probe function - snp_svsm_vtpm_probe() - and you're
>calling it in tpm_svsm_probe().
>
>So why aren't you registering the platform device there too but are doing this
>unconditional strange thing here?

We discussed a bit on v3, but I'm open to change it:
https://lore.kernel.org/linux-integrity/nrn4ur66lz2ocbkkjl2bgiex3xbp552szerfhalsaefunqxf7p@ki7xf66zrf6u/

  I tried to keep the logic of whether or not the driver is needed all in 
  the tpm_svsm_probe()/snp_svsm_vtpm_probe() (where I check for SVSM).
  If you prefer to move some pieces here, though, I'm open.

Thanks,
Stefano