linux-kernel - Re: [PATCH 2/2] spi: spi-qcom-qspi: Add DMA mode support

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Message-ID: <0eb8dbab-c76b-771f-5a99-3e548ec55731@quicinc.com>
Date:   Wed, 12 Apr 2023 22:57:48 +0530
From:   Vijaya Krishna Nivarthi <quic_vnivarth@...cinc.com>
To:     Mark Brown <broonie@...nel.org>
CC:     <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <vkoul@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <quic_msavaliy@...cinc.com>, <dianders@...omium.org>,
        <mka@...omium.org>, <swboyd@...omium.org>,
        <quic_vtanuku@...cinc.com>
Subject: Re: [PATCH 2/2] spi: spi-qcom-qspi: Add DMA mode support


On 4/12/2023 9:42 PM, Mark Brown wrote:
> On Wed, Apr 12, 2023 at 08:59:06PM +0530, Vijaya Krishna Nivarthi wrote:
>> On 4/6/2023 8:58 PM, Mark Brown wrote:
>>>>>> +	if (ctrl->xfer.dir == QSPI_READ)
>>>>>> +		byte_ptr = (uint8_t *)xfer->rx_buf;
>>>>>> +	else
>>>>>> +		byte_ptr = (uint8_t *)xfer->tx_buf;
>>>>> If we need to cast to or from void * there's some sort of problem.
>>>> the tx_buf is a const void*
>>>> in v2 I will cast for tx_buf only?
>>> Or just keep byte_ptr as const - we're not modifying it are we?
>> We are modifying it, hence did cast for tx_buf only
> If it's being modified won't that upset the callers that thought it was
> const and didn't expect the data to change?

I believe callers wouldn't be upset.

The byte_ptr is being modified (incremented)

It is initialised to tx_buf (a const*) and keeps getting incremented to 
parse data.

No data change.

That should be ok?