linux-kernel - Re: [PATCH v2 06/19] spi: dw: Discard static DW DMA slave structures

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Message-ID: <20200515123422.GZ185537@smile.fi.intel.com>
Date:   Fri, 15 May 2020 15:34:22 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Mark Brown <broonie@...nel.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Georgy Vlasov <Georgy.Vlasov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Allison Randal <allison@...utok.net>,
        Gareth Williams <gareth.williams.jx@...esas.com>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@...el.com>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "wuxu.wu" <wuxu.wu@...wei.com>, Clement Leger <cleger@...ray.eu>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/19] spi: dw: Discard static DW DMA slave structures

On Fri, May 15, 2020 at 01:47:45PM +0300, Serge Semin wrote:
> Having them declared is redundant since each struct dw_dma_chan has
> the same structure embedded and the structure from the passed dma_chan
> private pointer will be copied there as a result of the next calls
> chain:
> dma_request_channel() -> find_candidate() -> dma_chan_get() ->
> device_alloc_chan_resources() = dwc_alloc_chan_resources() ->
> dw_dma_filter().
> So just remove the static dw_dma_chan structures and use a locally
> declared data instance with dst_id/src_id set to the same values as
> the static copies used to have.

...

> -static struct dw_dma_slave mid_dma_tx = { .dst_id = 1 };
> -static struct dw_dma_slave mid_dma_rx = { .src_id = 0 };

> +	struct dw_dma_slave slave = {0};

I really would like to leave them separated and as in the original form, i.e.

	struct dw_dma_slave tx = { .dst_id = 1 };
	struct dw_dma_slave rx = { .src_id = 0 };

those src and dst IDs are put in that form on purpose...

> +	/* 1. Init rx channel (.src_id = 0, .dst_id = 0) */

...this comment adds a bit of confusion.
(Needs more time to parse and understand what IDs are in use)

> +	slave.dma_dev = &dma_dev->dev;
> +	dws->rxchan = dma_request_channel(mask, mid_spi_dma_chan_filter, &slave);

> +	/* 2. Init tx channel (.src_id = 0, .dst_id = 1) */

Ditto.

P.S. Just a recommendation for the future: in all your patches try to be less
invasive where it's possible.

-- 
With Best Regards,
Andy Shevchenko