linux-kernel - Re: [PATCH] soc: qcom: geni-se: Do not bother about enable/disable of interrupts in secondary sequencer for non-uart modes

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Date:   Wed, 14 Jun 2023 16:57:02 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>
CC:     <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_msavaliy@...cinc.com>,
        <mka@...omium.org>, <swboyd@...omium.org>,
        <quic_vtanuku@...cinc.com>
Subject: Re: [PATCH] soc: qcom: geni-se: Do not bother about enable/disable of
 interrupts in secondary sequencer for non-uart modes

Hi,


On 6/14/2023 12:44 AM, Doug Anderson wrote:
> Hi,
>
> On Tue, Jun 13, 2023 at 11:24 AM Vijaya Krishna Nivarthi
> <quic_vnivarth@...cinc.com> wrote:
>> Hi,
>>
>>
>> On 6/13/2023 11:27 PM, Doug Anderson wrote:
>>> Hi,
>>>
>>> On Tue, Jun 13, 2023 at 9:07 AM Vijaya Krishna Nivarthi
>>> <quic_vnivarth@...cinc.com> wrote:
>>>> Hi,
>>>>
>>>>
>>>> On 6/12/2023 7:09 PM, Vijaya Krishna Nivarthi wrote:
>>>>> Hi,
>>>>>
>>>>> Thank you very much for the review...
>>>>>
>>>>>
>>>>> On 6/7/2023 9:41 PM, Doug Anderson wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On Fri, Jun 2, 2023 at 11:13 AM Vijaya Krishna Nivarthi
>>>>>> <quic_vnivarth@...cinc.com> wrote:
>>>>>>> The select_fifo/dma_mode() functions in geni driver enable/disable
>>>>>>> interrupts (secondary included) conditionally for non-uart modes, while
>>>>>>> uart is supposed to manage this internally.
>>>>>>> However, only uart uses secondary IRQs while spi, i2c do not care about
>>>>>>> these at all making their enablement (or disablement) totally
>>>>>>> unnecessary
>>>>>>> for these protos.
>>>>>>>
>>>>>>> Drop enabling/disabling secondary IRQs for non-uart modes.
>>>>>>> This doesn't solve any observed problem but only gets rid of code
>>>>>>> pieces
>>>>>>> that are not required.
>>>>>>>
>>>>>>> Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
>>>>>>> ---
>>>>>>>     drivers/soc/qcom/qcom-geni-se.c | 24 ++++--------------------
>>>>>>>     1 file changed, 4 insertions(+), 20 deletions(-)
>>>>>> This seems like a nice cleanup to me. It's still odd that the general
>>>>>> code has a special case for UART, but I guess the alternative is to
>>>>>> duplicate the exact same logic for both the i2c and SPI drivers. I
>>>>>> won't insist on that, though I wouldn't be opposed to it either.
>>>>>>
>>>>>> I guess one comment, though: should we also remove the code that
>>>>>> messes with "SE_GENI_S_IRQ_EN" in geni_se_select_gpi_mode()?
>>>>> Right now we have gpi-dma mode support for i2c and spi but not for uart.
>>>>>
>>>>> Even when gpi-dma support is added, uart driver's interrupt handler
>>>>> would not be invoked so I believe it would be safe to drop that code
>>>>> from geni_se_select_gpi_mode() too.
>>>>>
>>>>> I will post v2 dropping same after some more lookup.
>>>> Looking at this once again, I am more inclined towards leaving alone
>>>> gpi_mode() for now.
>>>>
>>>> It probably needs cleanup but we want to take that up at a later time.
>>>>
>>>> Meanwhile its not causing much harm as we don't switch modes dynamically
>>>> for gpi case, so we are not losing much time there reading from and
>>>> writing to registers.
>>>>
>>>> Please let know your thoughts.
>>> It's not really about the time needed for the extra register writes,
>>> but just someone trying to understand the code who might be trying to
>>> figure out what bits are relevant. The bits related to the secondary
>>> sequencer's interrupts don't do anything useful when we're using the
>>> controller for i2c/spi, so why not delete them?
>>
>> Agreed the s_irqs are not useful for spi/i2c but Right now I am not
>> really sure how uart + gsi mode is going to look like.
>>
>> So how about we move the part that messes with s_irq in gpi_mode() into
>> a *if(proto == GENI_SE_UART)* conditional?
>>
>> Understand we are adding to weirdness but Would that be ok for now?
> For the non-GPI DMA path and for the PIO path we don't touch the
> "S_IRQ" for UART either (we don't touch any IRQs for the UART). ...so
> it doesn't seem right to be tweaking with the S_IRQ for UART. I would
> say delete it and if/when the UART needs GPI mode then we can figure
> out what to do.
>
> I'd actually wonder if GPI will ever be implemented for UART anyway.
> The whole idea of GPI is to allow sharing a port between more than one
> user. Each user could submit a "transaction" and they'd get the port
> for the duration of that transaction. After the transaction was done
> then another user would be able to grab the port. Typically UART isn't
> used like this. I'm not saying that it couldn't be done, but just
> saying that it would be a pretty non-standard way of using a UART...


Agreed on both.

Uploading v2 dropping from gpi_mode()

Thank you.

-Vijay/


>
> -Doug