From: Marc Dietrich <marvin24@gmx.de>
To: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Marc Dietrich <marvin24@gmx.de>,
linux-staging@lists.linux.dev, linux-tegra@vger.kernel.org,
gregkh@linuxfoundation.org, Thierry Reding <treding@nvidia.com>
Subject: Re: [PATCH] staging: nvec: make i2c controller register writes robust
Date: Wed, 1 May 2024 21:03:28 +0200 (CEST) [thread overview]
Message-ID: <79c10e8e-bf3e-7eca-a0cd-e177a270a517@gmx.de> (raw)
In-Reply-To: <2338e58b-1ec2-4500-9675-2d8a3aaa107f@codethink.co.uk>
Hi Ben,
On Mon, 22 Apr 2024, Ben Dooks wrote:
> On 21/04/2024 11:46, Marc Dietrich wrote:
>> The i2c controller needs to read back the data written to its registers.
>> This way we can avoid the long delay in the interrupt handler.
>>
>> Signed-off-by: Marc Dietrich <marvin24@gmx.de>
>> ---
>> drivers/staging/nvec/nvec.c | 41 ++++++++++++++++++++++---------------
>> 1 file changed, 24 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/staging/nvec/nvec.c b/drivers/staging/nvec/nvec.c
>> index 45df190c2f94..214839f51048 100644
>> --- a/drivers/staging/nvec/nvec.c
>> +++ b/drivers/staging/nvec/nvec.c
>> @@ -570,6 +570,22 @@ static void nvec_tx_set(struct nvec_chip *nvec)
>> (uint)nvec->tx->size, nvec->tx->data[1]);
>> }
>>
>> +/**
>> + * i2c_writel - safely write to an I2C client controller register
>> + * @val: value to be written
>> + * @reg: register to write to
>> + *
>> + * A write to an I2C controller register needs to be read back to make
>> sure
>> + * that the value has arrived.
>> + */
>> +static void i2c_writel(u32 val, void *reg)
>> +{
>> + writel_relaxed(val, reg);
>> +
>> + /* read back register to make sure that register writes completed */
>> + readl_relaxed(reg);
>> +}
>
> I thought the default behaviour of writel() should be to force writes
> out of any CPU buffers. Are there any bus isuses here causing the code
> to be necessary (and if so, why is there another buffer breaking the
> writel behaviour?)
if fear that's a question only NVIDIA can answer.
Marc
next prev parent reply other threads:[~2024-05-01 19:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-21 10:46 [PATCH] staging: nvec: make i2c controller register writes robust Marc Dietrich
2024-04-21 11:13 ` Greg KH
2024-04-21 18:44 ` Marc Dietrich
2024-04-22 11:29 ` Ben Dooks
2024-05-01 19:03 ` Marc Dietrich [this message]
2024-05-30 15:12 ` Thierry Reding
2024-05-20 8:11 ` Marc Dietrich
2024-05-20 8:52 ` Greg KH
2024-05-20 9:03 ` Greg KH
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