On Wed, Oct 25, 2017 at 01:46:33PM -0600, Jason Gunthorpe wrote:
> > struct tpm_chip *tpm_chip_find_get(u64 id)
> > {
> > struct tpm_chup *chip;
> > struct tpm_chip *res = NULL;
> > int chip_num = 0;
> > int chip_prev;
> >
> > mutex_lock(&idr_lock);
> >
> > do {
> > chip_prev = chip_num;
> >
> > chip = idr_get_next(&dev_nums_idr, &chip_num);
> >
> > if (chip && (!id || id == chip->id) && !tpm_try_get_ops(chip)) {
> > res = chip;
> > break;
> > }
> > } while (chip_prev != chip_num);
> >
> > mutex_unlock(&idr_lock);
> >
> > return res;
> > }
>
> ?? The old version was correct, idr_find_slowpath is better than an
> idr_get_next serach if you already know id.
>
> PrasannaKumar's solution seems right, if we already have chip, then we
> just need to lock it again:
>
> struct tpm_chip *tpm_chip_find_get(struct tpm_chip *chip)
> {
> struct tpm_chip *res = NULL;
>
> mutex_lock(&idr_lock);
>
> if (!chip) {
> int chip_num = 0;
> int chip_prev;
>
> do {
> chip_prev = chip_num;
> chip = idr_get_next(&dev_nums_idr, &chip_num);
> if (chip && !tpm_try_get_ops(chip)) {
> res = chip;
> break;
> }
> } while (chip_prev != chip_num);
> } else {
> if (!tpm_try_get_ops(chip))
> res = chip;
> }
>
> mutex_unlock(&idr_lock);
>
> return res;
> }
>
> Jason
The id has a nice feature that it is unique for one boot cycle you can
even try to get a chip that has been deleted. It has the most stable
properties in the long run.
Address is a reusable identifier in one boot cycle.
/Jarkko
