linux-kernel - Re: [PATCH v4 5/5] spi: spi-qcom-qspi: Add DMA mode support

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Message-ID: <7af39e18-dafe-b013-5e2d-ea33dd27cf17@quicinc.com>
Date:   Mon, 24 Apr 2023 15:00:49 +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>, <broonie@...nel.org>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <cros-qcom-dts-watchers@...omium.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <devicetree@...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 v4 5/5] spi: spi-qcom-qspi: Add DMA mode support

Hi,

Thank you very much for the review and all the inputs...


On 4/22/2023 1:28 AM, Doug Anderson wrote:
> On Fri, Apr 21, 2023 at 11:21 AM Vijaya Krishna Nivarthi
> <quic_vnivarth@...cinc.com> wrote:
>>>> If we were to have a linked list of descriptors that we can parse and
>>>> free, it would require 2 more fields
>>>>
>>>> this_descriptor_dma - dma address of the current descriptor
>>> Isn't that exactly the same value as "data_address"? Sure,
>>> "data_address" is a u32 and the DMA address is 64-bits, but elsewhere
>>> in the code you already rely on the fact that the upper bits of the
>>> DMA address are 0 when you do:
>>
>> No; data_address is the dma_address mapped to the xfer buffer.
>>
>> This is provided by spi framework and retrieved from sgl.
>>
>> "this_descriptor" would be the dma_address of the current cmd_descriptor.
>>
>> this is returned from dma_pool_alloc()
>>
>> this would be required for freeing.
> Oh! Of course, that's right. So you are correct, you'd need to add
> "this_descriptor_dma", but not the virtual address since that would be
> the same as the address of the structure via the list_node_t. I guess
> I won't insist on using a linked list even though it seems more
> elegant to me. In the very least it should fall back to PIO if the
> array isn't enough and if we need to change it later we always can.
>
> -Doug


Retained the array, addressed all other comments and uploaded v5.

Conditional can_dma() and clearing interrupts in handle_err(), I thought 
were particularly helpful as they were potential problems later.

test script was very useful too.

Thank you.