linux-kernel - Re: [PATCH -next 2/2] i2c: designware: Add support for new SoCs in AMDPSP driver

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Date:   Sun, 19 Mar 2023 19:16:49 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     Mark Hasemeyer <markhas@...omium.org>, jsd@...ihalf.com
Cc:     andriy.shevchenko@...ux.intel.com, jarkko.nikula@...ux.intel.com,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        rrangel@...omium.org, upstream@...ihalf.com, wsa@...nel.org,
        dabros@...gle.com
Subject: Re: [PATCH -next 2/2] i2c: designware: Add support for new SoCs in
 AMDPSP driver


On 3/17/23 14:18, Mark Hasemeyer wrote:
> -	/* Status field in command-response buffer is updated by PSP */
> -	status = READ_ONCE(req->hdr.status);
> +	if (req) {
> +		/* Status field in command-response buffer is updated by PSP */
> +		status = READ_ONCE(req->hdr.status);
> +	} else {
> +		status = psp_smn_read(PSP_MBOX_CMD_OFFSET, &status);
> +		status &= ~PSP_MBOX_FIELDS_READY;
> +	}
>
> The value of the mbox cmd register is getting clobbered by the return value
> from psp_smn_read. This can cause bus arbitration to fail as the driver will
> think it can grab the bus when it's actually in use by the PSP.

Mark - FYI this approach is being superseded by another patch series 
that instead uses MMIO from the CCP driver.

It would be better to comment on that series.

https://lore.kernel.org/linux-i2c/20230310211954.2490-9-mario.limonciello@amd.com/