Re: [PATCH RFC 0/6] mmc: renesas_sdhi: add support for DMA end irqs

["Arnd Bergmann" <arnd@arndb.de>]

On Tue, Oct 25, 2022, at 12:51, Ulf Hansson wrote:
> Hi Wolfram,
>
> On Thu, 6 Oct 2022 at 21:05, Wolfram Sang
> <wsa+renesas@sang-engineering.com> wrote:
>>
>> Motivation for this series from patch 5:
>>
>> ===
>> So far, we have been relying on access_end interrupts only to mark DMA
>> transfers as done implying that DMA end interrupts have occurred by then
>> anyhow. On some SoCs under some conditions, this turned out to be not
>> enough. So, we enable DMA interrupts as well and make sure that both
>> events, DMA irq and access_end irq, have happened before finishing the
>> DMA transfer.
>
> The tmio/sdhi core still relies on using tasklets. I think we should
> strive to move away from tasklets for all mmc host drivers and to use
> threaded irqs instead.
>
> That said, I am worried that it might be harder to move away from
> tasklets beyond $subject series, for tmio/sdhi, but I might be wrong?
> So, I am wondering if it perhaps would be better to make that
> modernization/conversion as the first step instead?

Moving away from tasklets is probably a good idea overall, but I'm
not sure that MMC actually needs a custom IRQ deferral mechanism
in addition to the existing BLOCK_SOFTIRQ. I would expect that block
drivers usually operate in the context of the blk_mq caller, and
adding in another thread context can add substantial latency.

    Arnd