Re: STMicroelectronics accelerometers driver.

[Jonathan Cameron <jic23@kernel.org>]

On 11/23/2012 04:10 PM, Denis CIOCCA wrote:
> Hi Jonathan and Lars-Peter,
>
> I have modified the source code but I am not sure if the spi dma code
> management is correctly because this part is new for me.
Comments on that below. It's much simpler than what you have done.
>
> About the complexity of channels management in the buffer code, I think
> the code is not too difficult and it is possible leave this code as now.
> Are you agree?
Yeah, that bit is fine.
>
>
> I attach the patch.
>
> Best regards,
>
> Denis
>
>

...
> diff --git a/drivers/iio/accel/st_accel_spi.c
> b/drivers/iio/accel/st_accel_spi.c
> new file mode 100644
> index 0000000..fbc199d
> --- /dev/null
> +++ b/drivers/iio/accel/st_accel_spi.c
> @@ -0,0 +1,178 @@
> +/*
> + * STMicroelectronics accelerometers driver
> + *
> + * Copyright 2012 STMicroelectronics Inc.
> + *
> + * Denis Ciocca <denis.ciocca@st.com>
> + *
> + * Licensed under the GPL-2.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/spi/spi.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/trigger.h>
> +
> +#include <linux/iio/accel/st_accel.h>
> +
> +
> +#define ACC_SPI_READ           0x80;
> +#define ACC_SPI_MULTIREAD      0xc0
> +
> +static int st_accel_spi_read(struct st_accel_data *adata,
> +                                               u8 reg_addr, int len, u8 *data)
> +{
> +       struct spi_message msg;
> +       int err;
This is on the stack. Needs to be on the heap to ensure alignment
and either it has to be on it's own or alignment to a cacheline
must be enforced.

u8 *tx = kmalloc(sizeof(tx), GFP_KERNEL);

Also note that data must also be dynamically allocated (from a quick
look it is).
> +       u8 tx;
> +
> +       struct spi_transfer xfers[] = {
> +               {
> +                       .tx_buf = &tx,
> +                       .bits_per_word = 8,
> +                       .len = 1,
> +               },
> +               {
> +                       .rx_buf = data,
> +                       .bits_per_word = 8,
> +                       .len = len,
> +               }
> +       };
> +
> +       if ((adata->multiread_bit == true) && (len > 1))
> +               tx = reg_addr | ACC_SPI_MULTIREAD;
> +       else
> +               tx = reg_addr | ACC_SPI_READ;
> +
> +       spi_message_init(&msg);
> +       spi_message_add_tail(&xfers[0], &msg);
> +       spi_message_add_tail(&xfers[1], &msg);
> +       err = spi_sync(to_spi_device(adata->dev), &msg);
> +       if (err)
> +               goto acc_spi_read_error;
> +
> +       return len;
> +
> +acc_spi_read_error:
> +       return err;
> +}
> +
> +static int st_accel_spi_read_byte(struct st_accel_data *adata,
> +                                               u8 reg_addr, u8 *res_byte)
> +{
> +       return st_accel_spi_read(adata, reg_addr, 1, res_byte);
> +}
> +
> +static int st_accel_spi_read_multiple_byte(struct st_accel_data *adata,
> +                                               u8 reg_addr, int len, u8 *data)
> +{
> +       return st_accel_spi_read(adata, reg_addr, len, data);
> +}
> +
> +static int st_accel_spi_write_byte(struct st_accel_data *adata,
> +                                                       u8 reg_addr, u8 data)
> +{
> +       struct spi_message msg;
> +       int err;
> +       u8 tx[2], *data_write;
> +

Errr.  Not sure what you are up to. It's simply a case of allocating
tx on the heap, not the stack.  This is true for anything that goes
in tx_buf or rx_buf of an spi_transfer structure;


struct spi_transfer xfers = {
       .bits_per_word = 8,
       .len = 2,
};
u8 *tx;

tx = kmalloc(sizeof(u8)*2);
tx[0] = reg_addr;
tx[1] = data_write;
xfers.tx_buf = tx;
...


kfree(tx);
}
> +       struct spi_transfer xfers = {
> +               .tx_buf = tx,
> +               .bits_per_word = 8,
> +               .len = 2,
> +       };
> +
> +       data_write = kmalloc(sizeof(*data_write), GFP_KERNEL);
> +       if (data_write == NULL) {
> +               err = -ENOMEM;
> +               goto alloc_memory_error;
> +       }
> +       *data_write = data;
> +
> +       tx[0] = reg_addr;
> +       tx[1] = *data_write;
> +       spi_message_init(&msg);
> +       spi_message_add_tail(&xfers, &msg);
> +       err = spi_sync(to_spi_device(adata->dev), &msg);
> +       kfree(data_write);
> +
> +alloc_memory_error:
> +       return err;
> +}
> +
...