linux-kernel - Re: [PATCH v4 1/6] tpm, tpm_tis

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Date:   Mon, 16 May 2022 21:52:05 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     peterhuewe@....de, jgg@...pe.ca, stefanb@...ux.vnet.ibm.com,
        linux@...ewoehner.de, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, lukas@...ner.de,
        p.rosenberger@...bus.com, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH v4 1/6] tpm, tpm_tis_spi: Request threaded irq

Hi,

On 13.05.22 at 20:08, Jarkko Sakkinen wrote:
> On Wed, May 11, 2022 at 09:18:39PM +0200, Lino Sanfilippo wrote:
>> Hi,
>>
>> On 11.05.22 at 13:22, Jarkko Sakkinen wrote:
>>> On Mon, May 09, 2022 at 10:05:54AM +0200, Lino Sanfilippo wrote:
>>>> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>>>
>>>> Interrupt handling at least includes reading and writing the interrupt
>>>> status register within the interrupt routine. Since accesses over the SPI
>>>> bus are synchronized by a mutex, request a threaded interrupt handler to
>>>> ensure a sleepable context during interrupt processing.
>>>>
>>>> Fixes: 1a339b658d9d ("tpm_tis_spi: Pass the SPI IRQ down to the driver")
>>>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>>
>>> When you state that it needs a sleepable context, you should bring a
>>> context why it needs it. This not to disregard the code change overally but
>>> you cannot make even the most obvious claim without backing data.
>>>
>>
>> so what kind of backing data do you have in mind? Would it help to emphasize more
>> that the irq handler is running in hard irq context in the current code and thus
>> must not access registers over SPI since SPI uses a mutex (I consider it as basic
>> knowledge that a mutex must not be taken in hard irq context)?
>
> There's zero mention about specific lock you are talking about. Providing
> the basic knowledge what you are trying to do is the whole point of the
> commit message in the first place. I'd presume this patch is related to the
> use bus_lock_mutex but it is fully ingored here.
>

Ok, understood. I will amend the commit message to make more clear that
reading and writing registers from the interrupt handler results in
a call to tpm_tis_spi_transfer() which uses the bus_lock_mutex of the
spi device and thus requires a sleepable context.


Regards,
Lino



> BR, Jarkko
>