Message-ID: <24b3ef71-18c1-1704-e324-5581fd18a998@codeaurora.org>
Date:   Mon, 21 May 2018 09:52:47 -0600
From:   "Mahadevan, Girish" <girishm@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>, broonie@...nel.org,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Cc:     sdharia@...eaurora.org, kramasub@...eaurora.org,
        dianders@...omium.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] spi: spi-geni-qcom: Add SPI driver support for GENI based
 QUP

Hi Stephen

On 5/11/2018 4:30 PM, Stephen Boyd wrote:

>> +       if (mode & SPI_CPHA)
>> +               cpha |= CPHA;
>> +
>> +       if (spi_slv->mode & SPI_CS_HIGH)
>> +               demux_output_inv |= BIT(spi_slv->chip_select);
>> +
>> +       if (spi_slv->controller_data) {
>> +               u32 cs_clk_delay = 0;
>> +               u32 inter_words_delay = 0;
>> +
>> +               delay_params =
>> +               (struct spi_geni_qcom_ctrl_data *) spi_slv->controller_data;
>> +               cs_clk_delay =
>> +               (delay_params->spi_cs_clk_delay << SPI_CS_CLK_DELAY_SHFT)
>> +                                                       & SPI_CS_CLK_DELAY_MSK;
>> +               inter_words_delay =
>> +                       delay_params->spi_inter_words_delay &
>> +                                               SPI_INTER_WORDS_DELAY_MSK;
>> +               spi_delay_params =
>> +               (inter_words_delay | cs_clk_delay);
>> +       }
>> +
>> +       demux_sel = spi_slv->chip_select;
>> +       mas->cur_speed_hz = spi_slv->max_speed_hz;
> 
> Why can't you use clk_get_rate() instead? Or call clk_set_rate() with
> the rate you want the master clk to run at and then divide that down
> from there?

Not sure I follow, the intention is to run the controller clock based on
the slave's max frequency.

>> +
>> +       ret = pm_runtime_get_sync(mas->dev);
>> +       if (ret < 0) {
>> +               dev_err(mas->dev, "Error enabling SE resources\n");
>> +               pm_runtime_put_noidle(mas->dev);
>> +               goto exit_prepare_transfer_hardware;
>> +       } else {
>> +               ret = 0;
> 
> Does pm_runtime_get_sync() return anything besides 0 on success?

This will go away, since I will switch to using auto-runtime option
provided by the framework.

> 
>> +       }
>> +
>> +       if (unlikely(!mas->setup)) {
>> +               int proto = geni_se_read_proto(se);
>> +               unsigned int major;
>> +               unsigned int minor;
>> +               unsigned int step;
>> +
>> +               if (unlikely(proto != GENI_SE_SPI)) {
>> +                       dev_err(mas->dev, "Invalid proto %d\n", proto);
>> +                       return -ENXIO;
>> +               }
>> +               mas->tx_fifo_depth = geni_se_get_tx_fifo_depth(se);
>> +               mas->rx_fifo_depth = geni_se_get_rx_fifo_depth(se);
>> +               mas->tx_fifo_width = geni_se_get_tx_fifo_width(se);
>> +               geni_se_init(se, 0x0, (mas->tx_fifo_depth - 2));
> 
> Why 2? Drop extra parenthesis please.

This is what the hardware programming doc recommends, the parameter is
actually the rx_rfr_watermark, something that doesn't apply to non-UART
protocols.
(I will add a detailed comment)
 an else if.
> 
>> +                       m_param |= FRAGMENTATION;
>> +       }
>> +
>> +       mas->cur_xfer = xfer;
>> +       if (m_cmd & SPI_TX_ONLY) {
>> +               mas->tx_rem_bytes = xfer->len;
>> +               writel_relaxed(trans_len, se->base + SE_SPI_TX_TRANS_LEN);
>> +       }
>> +
>> +       if (m_cmd & SPI_RX_ONLY) {
>> +               writel_relaxed(trans_len, se->base + SE_SPI_RX_TRANS_LEN);
>> +               mas->rx_rem_bytes = xfer->len;
>> +       }
>> +       writel_relaxed(spi_tx_cfg, se->base + SE_SPI_TRANS_CFG);
>> +       geni_se_setup_m_cmd(se, m_cmd, m_param);
>> +       if (m_cmd & SPI_TX_ONLY)
>> +               writel_relaxed(mas->tx_wm, se->base + SE_GENI_TX_WATERMARK_REG);
> 
> This can't be combined with above m_cmd & SPI_TX_ONLY statement?

No, writing to this register should be done after we enqueue the command
to the GENI engine(the geni_se_setup_m_cmd), but some of the transaction
properties (length etc) should be setup before we enqueue the GENI command.
   setup_fifo_xfer(xfer, mas, slv->mode, spi);
>> +       timeout = wait_for_completion_timeout(&mas->xfer_done,
>> +                               msecs_to_jiffies(SPI_XFER_TIMEOUT_MS));
> 
> Can you implement the 'handle_err' for the controller and call
> spi_finalize_current_transfer() from the interrupt handler when the
> transfer completes? The completion variable stuff and timeout code in
> this driver can hopefully all go away.

Will do (thanks for the suggestion).

> 
> More things can be unsigned?
> 
>> +               fifo_byte = (u8 *)&fifo_word;
>> +               for (j = 0; j < bytes_to_write; j++)
>> +                       fifo_byte[j] = tx_buf[i++];
> 
> Why are we doing all this work to fill in a fifo byte at a time? tx_buf
> should be a buffer of bytes that we can iowrite32_rep() with directly.
> And then we could just run iowrite32_rep() with some count of bytes to
> write? I suppose we may run into problems with unaligned size buffers,
> but it sounds like that doesn't happen?

I did this for 2 reasons.
1.The core can handle different byte order transmissions (e.g MSB
first), I am quite honestly not sure how the client's will setup the
data buffer in these cases.(for bigger word sizes , 16/32)
[we plan to support these]
2. For non-byte aligned word sizes (e,g 9), I am not enabling FIFO word
packing (meaning 1 SPI-WORD/FIFO-WORD in these cases).


>> +++ b/include/linux/spi/spi-geni-qcom.h
>> @@ -0,0 +1,14 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> 
> Why?
> 
>> +/*
>> + * Copyright (c) 2017-2018, The Linux Foundation. All rights reserved.
>> + */
>> +
>> +#ifndef __SPI_GENI_QCOM_HEADER___
>> +#define __SPI_GENI_QCOM_HEADER___
>> +
>> +struct spi_geni_qcom_ctrl_data {
> 
> What's the point of this header file and structure? This driver supports
> board files? Isn't everything DT now?

The intention was to allow a client to specify slave specific timing
requirements, e.g CS-CLK delay (based on the slave's data sheet).
So that the client drivers could setup these delays and pass it in part
of the controller_data member of the spi_device data structure.
The header file was meant to expose these timing params that the client
could specify. I honestly didn't know how else a client could specify
these to the controller driver.

> 
>> +       u32 spi_cs_clk_delay;
>> +       u32 spi_inter_words_delay;
>> +};
>> +

Best Regards
Girish

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