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Subject: Re: [PATCH v4 1/6] tpm, tpm_tis_spi: Request threaded irq
To:     Jarkko Sakkinen <jarkko@kernel.org>
Cc:     peterhuewe@gmx.de, jgg@ziepe.ca, stefanb@linux.vnet.ibm.com,
        linux@mniewoehner.de, linux-integrity@vger.kernel.org,
        linux-kernel@vger.kernel.org, lukas@wunner.de,
        p.rosenberger@kunbus.com, Lino Sanfilippo <l.sanfilippo@kunbus.com>
References: <20220509080559.4381-1-LinoSanfilippo@gmx.de>
 <20220509080559.4381-2-LinoSanfilippo@gmx.de> <YnucgDH3I87RI8PN@kernel.org>
 <486cec01-ec02-3f11-0b81-037e0700c503@gmx.de> <Yn6esMyUl+QhECq+@kernel.org>
From:   Lino Sanfilippo <LinoSanfilippo@gmx.de>
Message-ID: <1b306d56-c6b3-e51f-1d63-2f6725fa7557@gmx.de>
Date:   Mon, 16 May 2022 21:52:05 +0200
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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@kunbus.com>
>>>>
>>>> Interrupt handling at least includes reading and writing the interrup=
t
>>>> 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 drive=
r")
>>>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.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 overall=
y 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 emph=
asize 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 i=
t 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. Providin=
g
> 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
>