Re: [PATCH v2 3/3] mmc: Add driver for LiteX's LiteSDCard interface

Geert Uytterhoeven
2021-12-06T10:08:18Z

Hi Gabriel,

On Sat, Dec 4, 2021 at 9:41 PM Gabriel Somlo <gsomlo@gmail.com> 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@antmicro.com>
> Signed-off-by: Kamil Rakoczy <krakoczy@antmicro.com>
> Co-developed-by: Maciej Dudek <mdudek@internships.antmicro.com>
> Signed-off-by: Maciej Dudek <mdudek@internships.antmicro.com>
> Co-developed-by: Paul Mackerras <paulus@ozlabs.org>
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>

Thanks for your patch!

> --- /dev/null
> +++ b/drivers/mmc/host/litex_mmc.c

> +struct litex_mmc_host {
> + struct mmc_host *mmc;
> + struct platform_device *dev;
> +
> + void __iomem *sdphy;
> + void __iomem *sdcore;
> + void __iomem *sdreader;
> + void __iomem *sdwriter;
> + void __iomem *sdirq;
> +
> + u32 resp[4];
> + u16 rca;
> +
> + void *buffer;
> + size_t buf_size;
> + dma_addr_t dma;
> +
> + unsigned int freq;
> + unsigned int clock;
> + bool is_bus_width_set;
> + bool app_cmd;
> +
> + int irq;
> + struct completion cmd_done;

You may want to reorder the members to avoid implicit gaps
(i.e. structs first, followed by integral types in decreasing size).

> +};
> +
> +static int
> +sdcard_wait_done(void __iomem *reg)
> +{
> + u8 evt;
> + int ret;
> +
> + ret = read_poll_timeout(litex_read8, evt, (evt & 0x1),

Lots of magic numbers. Please use defines, like

#define EVT_FOO BIT(0)

> + SD_SLEEP_US, SD_TIMEOUT_US, false, reg);
> + if (ret || (evt & 0x4))
> + return SD_TIMEOUT;
> + if (evt == 0x1)
> + return SD_OK;
> + if (evt & 0x2)
> + return SD_WRITEERROR;
> + if (evt & 0x8)
> + return SD_CRCERROR;
> + pr_err("%s: unknown error evt=%x\n", __func__, evt);
> + return SD_ERR_OTHER;
> +}
> +
> +static int
> +send_cmd(struct litex_mmc_host *host,
> + u8 cmd, u32 arg, u8 response_len, u8 transfer)
> +{
> + void __iomem *reg;
> + u8 i;

unsigned int

> + int status;
> +
> + litex_write32(host->sdcore + LITEX_CORE_CMDARG, arg);
> + litex_write32(host->sdcore + LITEX_CORE_CMDCMD,
> + cmd << 8 | transfer << 5 | response_len);
> + litex_write8(host->sdcore + LITEX_CORE_CMDSND, 1);
> +
> + /* Wait for an interrupt if we have an interrupt and either there is
> + * data to be transferred, or if the card can report busy via DAT0.
> + */
> + if (host->irq > 0 &&
> + (transfer != SDCARD_CTRL_DATA_TRANSFER_NONE ||
> + response_len == SDCARD_CTRL_RESPONSE_SHORT_BUSY)) {
> + reinit_completion(&host->cmd_done);
> + litex_write32(host->sdirq + LITEX_IRQ_ENABLE,
> + SDIRQ_CMD_DONE | SDIRQ_CARD_DETECT);
> + wait_for_completion(&host->cmd_done);
> + }
> +
> + status = sdcard_wait_done(host->sdcore + LITEX_CORE_CMDEVT);
> +
> + if (status != SD_OK) {
> + pr_err("Command (cmd %d) failed, status %d\n", cmd, status);
> + return status;
> + }
> +
> + if (response_len != SDCARD_CTRL_RESPONSE_NONE) {
> + reg = host->sdcore + LITEX_CORE_CMDRSP;
> + for (i = 0; i < 4; i++) {
> + host->resp[i] = litex_read32(reg);
> + reg += sizeof(u32);
> + }
> + }
> +
> + if (!host->app_cmd && cmd == SD_SEND_RELATIVE_ADDR)
> + host->rca = (host->resp[3] >> 16) & 0xffff;
> +
> + host->app_cmd = (cmd == MMC_APP_CMD);
> +
> + if (transfer == SDCARD_CTRL_DATA_TRANSFER_NONE)
> + return status; /* SD_OK from prior sdcard_wait_done(cmd_evt) */
> +
> + status = sdcard_wait_done(host->sdcore + LITEX_CORE_DATAEVT);
> + if (status != SD_OK) {
> + pr_err("Data xfer (cmd %d) failed, status %d\n", cmd, status);
> + return status;
> + }
> +
> + /* wait for completion of (read or write) DMA transfer */
> + reg = (transfer == SDCARD_CTRL_DATA_TRANSFER_READ) ?
> + host->sdreader + LITEX_BLK2MEM_DONE :
> + host->sdwriter + LITEX_MEM2BLK_DONE;
> +
> + status = read_poll_timeout(litex_read8, i, (i & 0x1),
> + SD_SLEEP_US, SD_TIMEOUT_US, false, reg);
> + if (status)
> + pr_err("DMA timeout (cmd %d)\n", cmd);
> +
> + return status;
> +}
> +
> +static inline int

No need for inline, the compiler can decide.

> +send_app_cmd(struct litex_mmc_host *host)
> +{
> + return send_cmd(host, MMC_APP_CMD, host->rca << 16,
> + SDCARD_CTRL_RESPONSE_SHORT,
> + SDCARD_CTRL_DATA_TRANSFER_NONE);
> +}
> +
> +static inline int

Likewise.

> +send_app_set_bus_width_cmd(struct litex_mmc_host *host, u32 width)
> +{
> + return send_cmd(host, SD_APP_SET_BUS_WIDTH, width,
> + SDCARD_CTRL_RESPONSE_SHORT,
> + SDCARD_CTRL_DATA_TRANSFER_NONE);
> +}

> +static int
> +litex_get_cd(struct mmc_host *mmc)

litex_mmc_get_cd()? (i.e. "litex_mmc_"-prefix everywhere)

> +{
> + struct litex_mmc_host *host = mmc_priv(mmc);
> + int ret;
> +
> + if (!mmc_card_is_removable(mmc))
> + return 1;
> +
> + ret = mmc_gpio_get_cd(mmc);
> + if (ret >= 0)
> + /* GPIO based card-detect explicitly specified in DTS */
> + ret = !!ret;
> + else
> + /* use gateware card-detect bit by default */
> + ret = !litex_read8(host->sdphy + LITEX_PHY_CARDDETECT);

Please use curly braces to delimit blocks larger than a single line.

> +
> + /* ensure bus width will be set (again) upon card (re)insertion */
> + if (ret == 0)
> + host->is_bus_width_set = false;
> +
> + return ret;
> +}

> +static u32
> +litex_response_len(struct mmc_command *cmd)
> +{
> + if (cmd->flags & MMC_RSP_136) {
> + return SDCARD_CTRL_RESPONSE_LONG;
> + } else if (cmd->flags & MMC_RSP_PRESENT) {

No need for else after return.

> + if (cmd->flags & MMC_RSP_BUSY)
> + return SDCARD_CTRL_RESPONSE_SHORT_BUSY;
> + else
> + return SDCARD_CTRL_RESPONSE_SHORT;
> + }
> + return SDCARD_CTRL_RESPONSE_NONE;

Perhaps it's worthwhile to invert the logic of the last check, to
reduce indentation?

if (cmd->flags & MMC_RSP_136)
return SDCARD_CTRL_RESPONSE_LONG;

if (!(cmd->flags & MMC_RSP_PRESENT))
return SDCARD_CTRL_RESPONSE_NONE;

if (cmd->flags & MMC_RSP_BUSY)
return SDCARD_CTRL_RESPONSE_SHORT_BUSY;

return SDCARD_CTRL_RESPONSE_SHORT;

> +}

> +static void
> +litex_request(struct mmc_host *mmc, struct mmc_request *mrq)
> +{
> + struct litex_mmc_host *host = mmc_priv(mmc);
> + struct platform_device *pdev = to_platform_device(mmc->parent);
> + struct device *dev = &pdev->dev;
> + struct mmc_data *data = mrq->data;
> + struct mmc_command *sbc = mrq->sbc;
> + struct mmc_command *cmd = mrq->cmd;
> + struct mmc_command *stop = mrq->stop;
> + unsigned int retries = cmd->retries;
> + int status;
> + int sg_count;
> + enum dma_data_direction dir = DMA_TO_DEVICE;
> + bool direct = false;
> + dma_addr_t dma;
> + unsigned int len = 0;

The above might look nicer when using "reverse Xmas tree" order
of declarations.

> +
> + u32 response_len = litex_response_len(cmd);
> + u32 transfer = SDCARD_CTRL_DATA_TRANSFER_NONE;
> +
> + /* First check that the card is still there */
> + if (!litex_get_cd(mmc)) {
> + cmd->error = -ENOMEDIUM;
> + mmc_request_done(mmc, mrq);
> + return;
> + }
> +
> + /* Send set-block-count command if needed */
> + if (sbc) {
> + status = send_cmd(host, sbc->opcode, sbc->arg,
> + litex_response_len(sbc),
> + SDCARD_CTRL_DATA_TRANSFER_NONE);
> + sbc->error = litex_map_status(status);
> + if (status != SD_OK) {
> + host->is_bus_width_set = false;
> + mmc_request_done(mmc, mrq);
> + return;
> + }
> + }
> +
> + if (data) {
> + /* 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!
> + */
> + if (!host->is_bus_width_set) {
> + ulong n = jiffies + 2 * HZ; // 500ms timeout
> +
> + while (litex_set_bus_width(host) != SD_OK) {
> + if (time_after(jiffies, n)) {
> + dev_warn(dev, "Can't set bus width!\n");
> + cmd->error = -ETIMEDOUT;
> + mmc_request_done(mmc, mrq);
> + return;
> + }
> + }
> + host->is_bus_width_set = true;
> + }
> +
> + /* Try to DMA directly to/from the data buffer.
> + * We can do that if the buffer can be mapped for DMA
> + * in one contiguous chunk.
> + */
> + dma = host->dma;
> + len = data->blksz * data->blocks;
> + if (data->flags & MMC_DATA_READ)
> + dir = DMA_FROM_DEVICE;
> + sg_count = dma_map_sg(&host->dev->dev,
> + data->sg, data->sg_len, dir);
> + if (sg_count == 1) {
> + dma = sg_dma_address(data->sg);
> + len = sg_dma_len(data->sg);
> + direct = true;
> + } else if (len > host->buf_size)
> + len = host->buf_size;
> +
> + if (data->flags & MMC_DATA_READ) {
> + litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 0);
> + litex_write64(host->sdreader + LITEX_BLK2MEM_BASE, dma);
> + litex_write32(host->sdreader + LITEX_BLK2MEM_LEN, len);
> + litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 1);
> +
> + transfer = SDCARD_CTRL_DATA_TRANSFER_READ;
> + } else if (data->flags & MMC_DATA_WRITE) {
> + if (!direct)
> + sg_copy_to_buffer(data->sg, data->sg_len,
> + host->buffer, len);
> +
> + litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 0);
> + litex_write64(host->sdwriter + LITEX_MEM2BLK_BASE, dma);
> + litex_write32(host->sdwriter + LITEX_MEM2BLK_LEN, len);
> + litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 1);
> +
> + transfer = SDCARD_CTRL_DATA_TRANSFER_WRITE;
> + } else {
> + dev_warn(dev, "Data present w/o read or write flag.\n");
> + /* Continue: set cmd status, mark req done */
> + }
> +
> + litex_write16(host->sdcore + LITEX_CORE_BLKLEN, data->blksz);
> + litex_write32(host->sdcore + LITEX_CORE_BLKCNT, data->blocks);
> + }
> +
> + do {
> + status = send_cmd(host, cmd->opcode, cmd->arg,
> + response_len, transfer);
> + } while (status != SD_OK && retries-- > 0);
> +
> + cmd->error = litex_map_status(status);
> + if (status != SD_OK)
> + /* card may be gone; don't assume bus width is still set */
> + host->is_bus_width_set = false;

Please add curly braces.

> +
> + if (response_len == SDCARD_CTRL_RESPONSE_SHORT) {
> + /* pull short response fields from appropriate host registers */
> + cmd->resp[0] = host->resp[3];
> + cmd->resp[1] = host->resp[2] & 0xFF;
> + } else if (response_len == SDCARD_CTRL_RESPONSE_LONG) {
> + cmd->resp[0] = host->resp[0];
> + cmd->resp[1] = host->resp[1];
> + cmd->resp[2] = host->resp[2];
> + cmd->resp[3] = host->resp[3];
> + }
> +
> + /* Send stop-transmission command if required */
> + if (stop && (cmd->error || !sbc)) {
> + int stop_stat;
> +
> + stop_stat = send_cmd(host, stop->opcode, stop->arg,
> + litex_response_len(stop),
> + SDCARD_CTRL_DATA_TRANSFER_NONE);
> + stop->error = litex_map_status(stop_stat);
> + if (stop_stat != SD_OK)
> + host->is_bus_width_set = false;
> + }
> +
> + if (data)
> + dma_unmap_sg(&host->dev->dev, data->sg, data->sg_len, dir);
> +
> + if (status == SD_OK && transfer != SDCARD_CTRL_DATA_TRANSFER_NONE) {
> + data->bytes_xfered = min(len, mmc->max_req_size);
> + if (transfer == SDCARD_CTRL_DATA_TRANSFER_READ && !direct) {
> + sg_copy_from_buffer(data->sg, sg_nents(data->sg),
> + host->buffer, data->bytes_xfered);
> + }
> + }
> +
> + mmc_request_done(mmc, mrq);
> +}
> +
> +static void
> +litex_set_clk(struct litex_mmc_host *host, unsigned int clk_freq)
> +{
> + u32 div = clk_freq ? host->freq / clk_freq : 256;
> +
> + div = roundup_pow_of_two(div);
> + div = min_t(u32, max_t(u32, div, 2), 256);

No need for the _t-variants if you make the constants unsigned (e.g. 2U).

> + dev_info(&host->dev->dev, "sdclk_freq=%d: set to %d via div=%d\n",
> + clk_freq, host->freq / div, div);
> + litex_write16(host->sdphy + LITEX_PHY_CLOCKERDIV, div);
> +}

> +static int
> +litex_mmc_probe(struct platform_device *pdev)
> +{
> + struct litex_mmc_host *host;
> + struct mmc_host *mmc;
> + struct device_node *cpu;
> + int ret;
> +
> + mmc = mmc_alloc_host(sizeof(struct litex_mmc_host), &pdev->dev);
> + /* 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;`
> + */
> + if (!mmc)
> + return -ENOMEM;
> +
> + host = mmc_priv(mmc);
> + host->mmc = mmc;
> + host->dev = pdev;
> +
> + host->clock = 0;
> + cpu = of_get_next_cpu_node(NULL);
> + ret = of_property_read_u32(cpu, "clock-frequency", &host->freq);
> + of_node_put(cpu);
> + if (ret) {
> + dev_err(&pdev->dev, "No \"clock-frequency\" property in DT\n");
> + goto err_free_host;
> + }
> +
> + init_completion(&host->cmd_done);
> + host->irq = platform_get_irq(pdev, 0);

platform_get_irq_optional()

So interrupts should not be required in the DT bindings.

> + if (host->irq < 0)
> + dev_err(&pdev->dev, "Failed to get IRQ, using polling\n");

This is not an error condition: dev_info() or dev_warn().

> +
> + /* 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;
> +
> + ret = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32));
> + if (ret)
> + goto err_free_host;
> +
> + host->buf_size = mmc->max_req_size * 2;
> + host->buffer = dma_alloc_coherent(&pdev->dev, host->buf_size,
> + &host->dma, GFP_DMA);
> + if (host->buffer == NULL) {
> + ret = -ENOMEM;
> + goto err_free_host;
> + }
> +
> + host->sdphy = devm_platform_ioremap_resource_byname(pdev, "phy");

So reg-names is required ;-)

> + if (IS_ERR(host->sdphy)) {
> + ret = PTR_ERR(host->sdphy);
> + goto err_free_dma;
> + }
> +
> + host->sdcore = devm_platform_ioremap_resource_byname(pdev, "core");
> + if (IS_ERR(host->sdcore)) {
> + ret = PTR_ERR(host->sdcore);
> + goto err_free_dma;
> + }
> +
> + host->sdreader = devm_platform_ioremap_resource_byname(pdev, "reader");
> + if (IS_ERR(host->sdreader)) {
> + ret = PTR_ERR(host->sdreader);
> + goto err_free_dma;
> + }
> +
> + host->sdwriter = devm_platform_ioremap_resource_byname(pdev, "writer");
> + if (IS_ERR(host->sdwriter)) {
> + ret = PTR_ERR(host->sdwriter);
> + goto err_free_dma;
> + }
> +
> + if (host->irq > 0) {
> + host->sdirq = devm_platform_ioremap_resource_byname(pdev, "irq");

So you need a "minItems: 4" for reg{,-names} in the DT bindings.

> + if (IS_ERR(host->sdirq)) {
> + ret = PTR_ERR(host->sdirq);
> + goto err_free_dma;
> + }
> + }
> +
> + mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;
> + mmc->ops = &litex_mmc_ops;
> +
> + mmc->f_min = 12.5e6;
> + mmc->f_max = 50e6;
> +
> + ret = mmc_of_parse(mmc);
> + if (ret)
> + goto err_free_dma;
> +
> + /* 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_FULL_PWR_CYCLE |
> + MMC_CAP2_NO_SDIO;
> +
> + platform_set_drvdata(pdev, host);
> +
> + ret = mmc_add_host(mmc);
> + if (ret < 0)
> + goto err_free_dma;
> +
> + /* ensure DMA bus masters are disabled */
> + litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 0);
> + litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 0);
> +
> + /* set up interrupt handler */
> + if (host->irq > 0) {
> + ret = request_irq(host->irq, litex_mmc_interrupt, 0,
> + "litex-mmc", mmc);
> + if (ret < 0) {
> + dev_err(&pdev->dev,
> + "irq setup error %d, using polling\n", ret);
> + host->irq = 0;
> + }
> + }
> +
> + /* enable card-change interrupts, or else ask for polling */
> + if (host->irq > 0) {
> + litex_write32(host->sdirq + LITEX_IRQ_PENDING,
> + SDIRQ_CARD_DETECT); /* clears it */
> + litex_write32(host->sdirq + LITEX_IRQ_ENABLE,
> + SDIRQ_CARD_DETECT);
> + } else {
> + mmc->caps |= MMC_CAP_NEEDS_POLL;
> + }
> +
> + return 0;
> +
> +err_free_dma:
> + dma_free_coherent(&pdev->dev, host->buf_size, host->buffer, host->dma);
> +err_free_host:
> + mmc_free_host(mmc);
> + return ret;
> +}

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds