Re: [PATCH v11 3/3] mmc: Add driver for LiteX's LiteSDCard interface

[Stafford Horne]

On Sun, Jan 09, 2022 at 06:20:03PM -0500, Gabriel Somlo wrote:
> LiteX (https://github.com/enjoy-digital/litex) is a SoC framework
> that targets FPGAs. LiteSDCard is a small footprint, configurable
> SDCard core commonly used in LiteX designs.
> 
> The driver was first written in May 2020 and has been maintained
> cooperatively by the LiteX community. Thanks to all contributors!
> 
> Co-developed-by: Kamil Rakoczy <krakoczy@xxxxxxxxxxxx>
> Signed-off-by: Kamil Rakoczy <krakoczy@xxxxxxxxxxxx>
> Co-developed-by: Maciej Dudek <mdudek@xxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Maciej Dudek <mdudek@xxxxxxxxxxxxxxxxxxxxxxxx>
> Co-developed-by: Paul Mackerras <paulus@xxxxxxxxxx>
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
> Signed-off-by: Gabriel Somlo <gsomlo@xxxxxxxxx>
> Reviewed-by: Joel Stanley <joel@xxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> ---
> 
...
> +static int litex_mmc_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct litex_mmc_host *host;
> +	struct mmc_host *mmc;
> +	struct clk *clk;
> +	int ret;
> +
> +	/*
> +	 * NOTE: defaults to max_[req,seg]_size=PAGE_SIZE, max_blk_size=512,
> +	 * and max_blk_count accordingly set to 8;
> +	 * If for some reason we need to modify max_blk_count, we must also
> +	 * re-calculate `max_[req,seg]_size = max_blk_size * max_blk_count;`
> +	 */
> +	mmc = mmc_alloc_host(sizeof(struct litex_mmc_host), dev);
> +	if (!mmc)
> +		return -ENOMEM;
> +
> +	ret = devm_add_action_or_reset(dev, litex_mmc_free_host_wrapper, mmc);
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Can't register mmc_free_host action\n");
> +
> +	host = mmc_priv(mmc);
> +	host->mmc = mmc;
> +
> +	/* Initialize clock source */
> +	clk = devm_clk_get(dev, NULL);
> +	if (IS_ERR(clk))
> +		return dev_err_probe(dev, PTR_ERR(clk), "can't get clock\n");
> +	host->ref_clk = clk_get_rate(clk);
> +	host->sd_clk = 0;
> +
> +	/*
> +	 * LiteSDCard only supports 4-bit bus width; therefore, we MUST inject
> +	 * a SET_BUS_WIDTH (acmd6) before the very first data transfer, earlier
> +	 * than when the mmc subsystem would normally get around to it!
> +	 */
> +	host->is_bus_width_set = false;
> +	host->app_cmd = false;
> +
> +	/* LiteSDCard can support 64-bit DMA addressing */
> +	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
> +	if (ret)
> +		return ret;
> +
> +	host->buf_size = mmc->max_req_size * 2;
> +	host->buffer = dmam_alloc_coherent(dev, host->buf_size,
> +					   &host->dma, GFP_KERNEL);
> +	if (host->buffer == NULL)
> +		return -ENOMEM;
> +
> +	host->sdphy = devm_platform_ioremap_resource_byname(pdev, "phy");
> +	if (IS_ERR(host->sdphy))
> +		return PTR_ERR(host->sdphy);
> +
> +	host->sdcore = devm_platform_ioremap_resource_byname(pdev, "core");
> +	if (IS_ERR(host->sdcore))
> +		return PTR_ERR(host->sdcore);
> +
> +	host->sdreader = devm_platform_ioremap_resource_byname(pdev, "reader");
> +	if (IS_ERR(host->sdreader))
> +		return PTR_ERR(host->sdreader);
> +
> +	host->sdwriter = devm_platform_ioremap_resource_byname(pdev, "writer");
> +	if (IS_ERR(host->sdwriter))
> +		return PTR_ERR(host->sdwriter);
> +
> +	/* Ensure DMA bus masters are disabled */
> +	litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 0);
> +	litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 0);
> +
> +	init_completion(&host->cmd_done);
> +	ret = litex_mmc_irq_init(pdev, host);
> +	if (ret)
> +		return ret;
> +
> +	/* Allow full generic 2.7-3.6V range; no software tuning available */
> +	mmc->ocr_avail = LITEX_MMC_OCR;
> +
> +	mmc->ops = &litex_mmc_ops;
> +
> +	/*
> +	 * Set default sd_clk frequency range based on empirical observations
> +	 * of LiteSDCard gateware behavior on typical SDCard media
> +	 */
> +	mmc->f_min = 12.5e6;
> +	mmc->f_max = 50e6;
> +
> +	ret = mmc_of_parse(mmc);
> +	if (ret)
> +		return ret;
> +
> +	/* Force 4-bit bus_width (only width supported by hardware) */
> +	mmc->caps &= ~MMC_CAP_8_BIT_DATA;
> +	mmc->caps |= MMC_CAP_4_BIT_DATA;
> +
> +	/* Set default capabilities */
> +	mmc->caps |= MMC_CAP_WAIT_WHILE_BUSY |
> +		     MMC_CAP_DRIVER_TYPE_D |
> +		     MMC_CAP_CMD23;
> +	mmc->caps2 |= MMC_CAP2_NO_WRITE_PROTECT |
> +		      MMC_CAP2_NO_SDIO |
> +		      MMC_CAP2_NO_MMC;
> +
> +	platform_set_drvdata(pdev, host);

One more thing here. Or somewhere, should we add:

	dev_info(dev, "Litex MMC controller initialized");

I was having a hard time debugging probing of this and having no printk's made
it a bit difficult.

Though I was able to get most of the debug statements I needed using:

	"debug initcall_debug dyndbg=\"file drivers/* +p\" loglevel=8"

-Stafford

> +	return mmc_add_host(mmc);
> +}
> +