linux-kernel - Re: [PATCH] tpm_tis_spi: Prefer async probe

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Message-ID: <20200623013614.GJ28795@linux.intel.com>
Date:   Tue, 23 Jun 2020 04:36:14 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Peter Huewe <peterhuewe@....de>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Andrey Pronin <apronin@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm_tis_spi: Prefer async probe

On Fri, Jun 19, 2020 at 02:20:01PM -0700, Douglas Anderson wrote:
> On a Chromebook I'm working on I noticed a big (~1 second) delay
> during bootup where nothing was happening.  Right around this big
> delay there were messages about the TPM:
> 
> [    2.311352] tpm_tis_spi spi0.0: TPM ready IRQ confirmed on attempt 2
> [    3.332790] tpm_tis_spi spi0.0: Cr50 firmware version: ...
> 
> I put a few printouts in and saw that tpm_tis_spi_init() (specifically
> tpm_chip_register() in that function) was taking the lion's share of
> this time, though ~115 ms of the time was in cr50_print_fw_version().
> 
> Let's make a one-line change to prefer async probe for tpm_tis_spi.
> There's no reason we need to block other drivers from probing while we
> load.
> 
> NOTES:
> * It's possible that other hardware runs through the init sequence
>   faster than Cr50 and this isn't such a big problem for them.
>   However, even if they are faster they are still doing _some_
>   transfers over a SPI bus so this should benefit everyone even if to
>   a lesser extent.
> * It's possible that there are extra delays in the code that could be
>   optimized out.  I didn't dig since once I enabled async probe they
>   no longer impacted me.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>  drivers/char/tpm/tpm_tis_spi_main.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/char/tpm/tpm_tis_spi_main.c b/drivers/char/tpm/tpm_tis_spi_main.c
> index d96755935529..422766445373 100644
> --- a/drivers/char/tpm/tpm_tis_spi_main.c
> +++ b/drivers/char/tpm/tpm_tis_spi_main.c
> @@ -288,6 +288,7 @@ static struct spi_driver tpm_tis_spi_driver = {
>  		.pm = &tpm_tis_pm,
>  		.of_match_table = of_match_ptr(of_tis_spi_match),
>  		.acpi_match_table = ACPI_PTR(acpi_tis_spi_match),
> +		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
>  	},
>  	.probe = tpm_tis_spi_driver_probe,
>  	.remove = tpm_tis_spi_remove,
> -- 
> 2.27.0.111.gc72c7da667-goog
> 


Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

/Jarkko