Re: [Qemu-devel] [PATCH v10 2/4] fw_cfg: do DMA read operation

[Marc-Andre Lureau]

Hi

On Wed, Jan 24, 2018 at 4:25 AM, Peter Xu <address@hidden> wrote:
> On Tue, Jan 23, 2018 at 05:40:39PM +0100, Marc-André Lureau wrote:
>> Modify fw_cfg_read_blob() to use DMA if the device supports it.
>> Return errors, because the operation may fail.
>>
>> The DMA operation is expected to run synchronously with today qemu,
>> but the specification states that it may become async, so we run
>> "control" field check in a loop for eventual changes.
>>
>> We may want to switch all the *buf addresses to use only kmalloc'ed
>> buffers (instead of using stack/image addresses with dma=false).
>>
>> Signed-off-by: Marc-André Lureau <address@hidden>
>> ---
>>  drivers/firmware/qemu_fw_cfg.c | 131 
>> ++++++++++++++++++++++++++++++++++-------
>>  1 file changed, 111 insertions(+), 20 deletions(-)
>>
>> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
>> index 740df0df2260..686f0e839858 100644
>> --- a/drivers/firmware/qemu_fw_cfg.c
>> +++ b/drivers/firmware/qemu_fw_cfg.c
>> @@ -33,6 +33,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/io.h>
>>  #include <linux/ioport.h>
>> +#include <linux/delay.h>
>>
>>  MODULE_AUTHOR("Gabriel L. Somlo <address@hidden>");
>>  MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
>> @@ -43,12 +44,22 @@ MODULE_LICENSE("GPL");
>>  #define FW_CFG_ID         0x01
>>  #define FW_CFG_FILE_DIR   0x19
>>
>> +#define FW_CFG_VERSION_DMA     0x02
>> +#define FW_CFG_DMA_CTL_ERROR   0x01
>> +#define FW_CFG_DMA_CTL_READ    0x02
>> +#define FW_CFG_DMA_CTL_SKIP    0x04
>> +#define FW_CFG_DMA_CTL_SELECT  0x08
>> +#define FW_CFG_DMA_CTL_WRITE   0x10
>> +
>>  /* size in bytes of fw_cfg signature */
>>  #define FW_CFG_SIG_SIZE 4
>>
>>  /* fw_cfg "file name" is up to 56 characters (including terminating nul) */
>>  #define FW_CFG_MAX_FILE_PATH 56
>>
>> +/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
>> +static u32 fw_cfg_rev;
>> +
>>  /* fw_cfg file directory entry type */
>>  struct fw_cfg_file {
>>       u32 size;
>> @@ -57,6 +68,12 @@ struct fw_cfg_file {
>>       char name[FW_CFG_MAX_FILE_PATH];
>>  };
>>
>> +struct fw_cfg_dma {
>> +     u32 control;
>> +     u32 length;
>> +     u64 address;
>> +} __packed;
>> +
>>  /* fw_cfg device i/o register addresses */
>>  static bool fw_cfg_is_mmio;
>>  static phys_addr_t fw_cfg_p_base;
>> @@ -75,12 +92,68 @@ static inline u16 fw_cfg_sel_endianness(u16 key)
>>       return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
>>  }
>>
>> +static inline bool fw_cfg_dma_enabled(void)
>> +{
>> +     return fw_cfg_rev & FW_CFG_VERSION_DMA && fw_cfg_reg_dma;
>> +}
>> +
>> +/* qemu fw_cfg device is sync today, but spec says it may become async */
>> +static void fw_cfg_wait_for_control(struct fw_cfg_dma *d)
>> +{
>> +     do {
>> +             u32 ctrl = be32_to_cpu(READ_ONCE(d->control));
>> +
>> +             if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0)
>> +                     return;
>> +
>> +             usleep_range(50, 100);
>> +     } while (true);
>> +}
>> +
>> +static ssize_t fw_cfg_dma_transfer(struct device *dev,
>> +                             void *address, u32 length, u32 control)
>> +{
>> +     phys_addr_t dma;
>> +     struct fw_cfg_dma *d = NULL;
>> +     ssize_t ret = length;
>> +
>> +     d = kmalloc(sizeof(*d), GFP_KERNEL);
>> +     if (!d) {
>> +             ret = -ENOMEM;
>> +             goto end;
>> +     }
>> +
>> +     *d = (struct fw_cfg_dma) {
>> +             .address = cpu_to_be64(virt_to_phys(address)),
>> +             .length = cpu_to_be32(length),
>> +             .control = cpu_to_be32(control)
>> +     };
>> +
>> +     dma = virt_to_phys(d);
>> +
>> +     iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
>> +     iowrite32be(dma, fw_cfg_reg_dma + 4);
>
> We can do it with iowrite64be(virt_to_phys(d)) too?  In all cases I
> think it's good enough and no worth for a repost.

That would not build on 32 bit, but we could have a #ifdef
CONFIG_64BIT (untested).

>
> For the DMA transfer part:
>
> Acked-by: Peter Xu <address@hidden>

thanks