Re: [PATCH 5/5] mmc: meson-gx: switch to descriptor chain mode

Kevin Hilman
2017-03-24T19:04:08Z

Hi Heiner,

Heiner Kallweit <hkallweit1@gmail.com> writes:

> Switch the driver from using a linearized bounce buffer to descriptor
> chain mode. This drastically improves performance.
>
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

I know this series needs a respin on top of your other cleanups, and
I'll have a closer look at it then, but one comment for the respin...

[...]

> static int meson_mmc_probe(struct platform_device *pdev)
> @@ -764,15 +790,14 @@ static int meson_mmc_probe(struct platform_device *pdev)
>
> mmc->caps |= MMC_CAP_CMD23;
> mmc->max_blk_count = CMD_CFG_LENGTH_MASK;
> - mmc->max_req_size = mmc->max_blk_count * mmc->max_blk_size;
> -
> - /* data bounce buffer */
> - host->bounce_buf_size = mmc->max_req_size;
> - host->bounce_buf =
> - dma_alloc_coherent(host->dev, host->bounce_buf_size,
> - &host->bounce_dma_addr, GFP_KERNEL);
> - if (host->bounce_buf == NULL) {
> - dev_err(host->dev, "Unable to map allocate DMA bounce buffer.\n");
> + mmc->max_segs = PAGE_SIZE / sizeof(struct sd_emmc_desc);
> + mmc->max_seg_size = mmc->max_blk_count * mmc->max_blk_size;
> + mmc->max_req_size = mmc->max_seg_size * mmc->max_segs;
> +
> + host->descs = dma_alloc_coherent(host->dev, PAGE_SIZE,
> + &host->descs_dma_addr, GFP_KERNEL);
> + if (!host->descs) {
> + dev_err(host->dev, "Allocating descriptor DMA buffer failed\n");
> ret = -ENOMEM;
> goto err_div_clk;
> }
> @@ -797,8 +822,8 @@ static int meson_mmc_remove(struct platform_device *pdev)
> /* disable interrupts */
> writel(0, host->regs + SD_EMMC_IRQ_EN);
>
> - dma_free_coherent(host->dev, host->bounce_buf_size,
> - host->bounce_buf, host->bounce_dma_addr);
> + dma_free_coherent(host->dev, PAGE_SIZE, host->descs,
> + host->descs_dma_addr);
>
> clk_disable_unprepare(host->cfg_div_clk);
> clk_disable_unprepare(host->core_clk);

Please replace the usage of PAGE_SIZE above with a #define at the top of
the driver for the max number of descriptors/segments. Right now, if
you wanted to change that, you'd have to change it in at least three
places.

Kevin